Aspect Ratio Of Nanorods Research Articles

Electrochemical and magnetic properties of α-MnO2:Dy nanorods

A facile hydrothermal technique with optimized condition used to synthesize single crystalline, α-MnO2 and α-MnO2:Dy nanorods of diameter 40 and 20 nm, respectively. We observe two fold magnitude higher specific capacitance (94 F g−1 at a scan rate of 10 mV/sec) in α-MnO2:Dy than that of α-MnO2 nanorods. X-ray diffraction (XRD) patterns while confirm the tetragonal structure in both compounds, decrease in crystallinity as well as aspect ratio of nanorods in α-MnO2:Dy contribute towards high capacitance. A decrease in Neel temperature (TN) from 24.5 K in bulk to 18 K in α-MnO2 nanorods further decreases to 11 K in α-MnO2:Dy nanorods. Addition to TN at 11 K, another magnetic anomaly at 4 K indicates Dy-Dy interaction. Although Dy incorporation enhances the antiferromagnetic strength as indicated from high Curie-Weiss temperature (θcw), exchange bias field significantly decreases and spin-glass behaviour is absent unlike in bare α-MnO2. Such magnetic features are well explained on the basis of core shell structure of nanorods where core is contributed by antiferromagnetic frozen spins and rotatable spins are contributed towards the surface. The competition between core and surface spins depending on the size of nanorods thus decides the spin-glass behaviour, EB field observed in these nanorods. Change in exchange bias field with consecutive cycles showing the training effect has been discussed after fitting with phenomenological models like Power law and multiple exponent function.

Effect of Dy on electrochemical supercapacitive behaviour of α-MnO2 nanorods

α-MnO2 nanorods doped with different molar concentrations of Dysprosium (Dy) have been successfully synthesised via hydrothermal method as an electrode material. The electrochemical properties are evaluated using cyclic voltammetry, Galvanostatic charge discharge studies where we demonstrate an increase in capacitance with increase in Dy concentration. For α-MnO2: Dy (15 mol %), capacitance enhances by twice than that of bare α-MnO2. XRD (X-Ray diffraction) and FE-SEM (Field Emission- Scanning Electron Microscopy) measurements show that although the structure of Dy doped α-MnO2 remains tetragonal, the crystallinity degrades along with the reduction in aspect ratio of nanorods. In addition, BET (Brunauer-Emmett-Teller) measurement shows that the surface area and size of the pores increase with increase in Dy concentration. Poor crystallinity, large surface area and smaller nanorods are an evidence of high capacitance observed in α-MnO2: Dy (15 mol %). The effect of Dy concentration on structure, morphology, surface area and electrochemical properties are discussed in detail for the application of supercapacitor.

Pulsed photoacoustic and photothermal response of gold nanoparticles

Gold nanospheres and nanorods are promising agents for photoacoustic imaging and photothermal therapy. In this work, seed-mediated methods were optimized for the synthesis of gold nanosphere and nanorod collides of different sizes. Nanosecond pulse photoacoustic and photothermal analysis of these nanoparticles was carried out and compared with finite element simulation. The simulations were performed to quantify the size dependent photoacoustic signal enhancement for nanospheres and nanorods. The non-sphericity contribution of nanospheres was found to enhance the photoacoustic signal. Nanosecond pulse photoacoustic studies of nanorods of different aspect ratio were carried out. Nanorods of aspect ratio ∼4.8 were found to be the most efficient photoacoustic signal generators. Photoacoustic studies of nanorods at varying laser fluence were performed and threshold fluence of 5 mJ cm−2 was observed. Nanorods exposed to nanosecond laser pulses underwent size and shape variations which were confirmed by optical absorbance and transmission electron microscopy measurements. Simulations of nanorods of different aspect ratio and diameter were performed to investigate the photoacoustic signal enhancement and photothermal stability. The miniature size nanorod with a diameter of 10 nm and aspect ratio of 5 was found to be most appropriate in terms of photoacoustic signal generation and photothermal stability.

Influence of High Aspect Ratio Lead‐Free Piezoelectric Fillers in Designing Flexible Fibrous Nanogenerators: Demonstration of Significant High Output Voltage

Engineering a flexible, cost‐effective piezoelectric energy harvester with a higher piezoelectric performance, i.e., higher voltage and power density, is a great technical challenge nowadays. Herein, the same target is set to demonstrate a unique nanogenerator comprising nanorods (aspect ratio of ≈8.5) of lead‐free potassium sodium niobate (KNN) and poly(vinylidene fluoride) (PVDF) where further poling process is fully omitted. The unique dimension of the synthesized rods with minimal loading (only 3%) bestows, somewhat surprisingly, a negative effect on beta nucleation but subdues this effect by the significant contribution toward the piezoelectric response by self‐orienting the dipoles at the electrospinning process by itself. Thus, the approach resolves the unmet task of complicacy in poling both the molecular and ionic dipoles at the same electric field in a subsequent poling of the finally formed nanocomposite. The nanodevice shows a higher open‐circuit output voltage of ≈17.5 V, an output current of ≈0.522 μA, and a current density of ≈0.13 μA cm−2 under repeated finger tapping and can power a light‐emitting diode (LED) of 2 V practically. The study opens a new route for excellent flexible piezoelectric nanogenerators for promising application in an enormous arena of self‐powering portable and wearable electronic gadgets.

Effects of the aspect ratio of ZnO nanorods on the performance of piezoelectric nanogenerators

Abstract This paper presents an investigation on the performance of ZnO nanorod (ZNR)-based piezoelectric nanogenerators (PENGs). ZNRs on the ZnO seed layer coated double-sided flexible polyethylene terephthalate (PET) at different molar concentrations (0.01, 0.05 and 0.1 M) were synthesized by controlling the aspect ratio (length/diameter) of ZNRs, that are closely related to the piezoelectric output potential voltage using a simple hydrothermal method. ZNR PENGs were fabricated with an opposite electrode of gold-coated PET (Au/PET), which was placed on both the top and bottom of the ZNR-coated double-sided PET. X-ray diffraction and field emission scanning electron microscopy images revealed that as the molar concentration increased, the orientation of the as-grown ZNRs became non-uniformly distributed along the c-axis and also along with the decreased aspect ratio. At a low molar concentration (0.01 M), the ZNR PENGs exhibited a relatively high output potential voltage (∼4.48 V) under an external pressing mass (500 g). The ZNR samples grown at 0.05 and 0.1 M exhibited a lower piezoelectric voltage 2.48 and 1.84 V, respectively. These results confirmed that ZNR PENGs with a small diameter, long length (i.e. high aspect ratio) and good alignment tend to be bent more easily for the efficient generation of the piezoelectric potential.

Tailored CsPbX3 Nanorods for Electron-Emission Nanodevices

Going beyond much cultivated photovoltaic aspects of all inorganic lead halide perovskite, here we explored electron field emission of CsPbX3 nanorods, where X represents different halides, specifically Cl, Br, and I. Starting with room-temperature preparation of different perovskite nanorods, we examined their electron-emission behavior and found CsPbI3 as best electron emitter among the synthesized samples, which showed that low work function and high aspect ratio drove the best emission performance. Aspect ratios of the CsPbI3 nanorods were tailored via alteration of processing temperature. Nanorods prepared at 90 °C possessing maximum aspect ratio delivered a current density of 133 μA/cm2 at 8 V/μm applied external field. With an expectation of gaining better emission performance from as-synthesized optimized nanorods, reduced graphene oxide (rGO) was further attached to them. Relying on the emission beneficial electronic features of rGO as-prepared CsPbI3-rGO composite delivered significantly improved electron emission performance with low turn-on field and high field enhancement value, which are much better than the individual structural blocks. Easy electron passage from the composite as a consequence of work function decrement as well as high field amplification at graphene basal plane supported by one-dimensional CsPbI3 nanorod renders improvement in field values. Experimentally observed electron emission result is further verified through electrostatic field distribution calculation using ANSYS software. Such results indicated the potential utility of these kinds of perovskite materials in field electron-emission nanodevices.

Investigation of thermal conductivity property of plasmonic nanofluids based on gold nanorods prepared by seed-mediated growth method

In this paper, nanofluids were prepared based on gold nanorods in basic fluid, water, by single-stage chemical reduction and in different volume fractions and the used gold nanorods were synthesized by seed-mediated growth method in different dimensional ratios. The properties of the prepared nanoparticles, including crystalline size, aspect ratio, surface properties, nanoparticle purity, shape and morphology of nanostructures were investigated using x-ray diffraction, UV-vis spectroscopy, FT-IR, and transmitted electron microscopy. The effect of changing parameters of Nano rod dimensions, changes in Nano rod volume fraction in water and also the effect of temperature on the nanofluid thermal conductivity coefficient were investigated using transient hot wire method. The results showed that reducing the aspect ratio, increasing the volume fraction and increasing the temperature increase the thermal conductivity. In fact, results show that an increase in the nanorods aspect ratio with a constant volume fraction of 1:50 of gold in water nanorod and at room temperature leads to a decrease in the thermal conductivity of the nanofluid. Also, increasing the two parameters of volume fraction and temperature significantly increases the thermal conductivity coefficient.

Bio-Inspired Synthesis of Non-Aqueous Liquid Crystals of Hydroxyapatite Nanorods

Hydroxyapatite (HA) nanorods in the collagen matrix of bone have a macroscopically ordered structure that has many similarities to the ordered structure of anisotropic nano-units in inorganic liquid crystals (LCs). Inspired by these similarities, we conducted the first (to our best knowledge) synthesis of HA LCs in non-polar solvents (such as cyclohexane and toluene), thus expanding the range of applicable monomers and polymers. We synthesized HA nanorods by a simple, effective, and oleic-acid-assisted hydrothermal route. The hydrothermal temperature directly modulates the aspect ratio of the HA nanorods, and indirectly modulates their LC behavior. The LC phase transition has no size limitation. Thus, our approach is a unique platform for developing high solid content, macroscopically assembled, large-scale polymer-based bio(mimetic)-materials.

Light Scattering, Absorption, and Refraction due to High-Order Optical Nonlinearities in Colloidal Gold Nanorods

We investigated the nonlinear (NL) optical behavior of aqueous colloidal dispersions of rod-shaped gold nanoparticles (NPs) with different aspect ratios beyond the usual analysis of third-order nonlinearity. By applying the Z-scan technique, it was possible to observe large NL absorption, which is understood by considering the simultaneous instantaneous and thermo-optical nonlinearity contributions. In addition, light-scattering experiments were performed at high intensities, showing a significant contribution of the fifth-order scattering process that depends on the gold nanorod (Au-NR) aspect ratio. Likewise, the Z-scan measurements reveal that the quintic nonlinearity is also contributing to the refractive behavior, a feature known for spherical gold NPs but not reported for Au-NRs so far. The experimental results illustrate a nonlinearity management procedure based on the strong influence of the aspect ratio of Au-NRs in the excitation regime close to the transverse surface plasmon resonance, even kee...

Morphology Controlled Synthesis of ZnO Nanorods for Glucose Enzymatic Biosensor

The use of zinc oxide nanorods is a promising option to increase the specific area for efficient glucose oxidase immobilization which further enhance the signal performance of glucose detection. In this work ZnO nanorods were prepared via hydrothermal process on sol-gel ZnO seed layer. The effects of different temperature of annealed seed layer on the morphology and properties of grow ZnO nanorods were investigated. The ZnO seed layers were annealed at various temperatures ranging from 300 to 600 °C for 2 h. The study demonstrated that the process condition of ZnO seed layer had a strong influence on the morphology and crystallinity of ZnO nanorods grow. X-ray diffraction analysis and scanning electronic microscopy were employed to characterize the crystal structure and morphology of the prepared ZnO seed layer and grow ZnO nanorods. The performance of different aspect ratio of ZnO nanorods on glucose detection were measured by using electrochemical analysis. With optimized ZnO nanorods, the glucose biosensor exhibited an enhanced in signal performance with a high sensitivity of 11.36 μA mM-1 cm-2 in the range of 0.05-1 mM. Such high performance was due to more immobilization on the well-aligned ZnO nanorods array and direct electron conduction between the nanorods and the electrodes

Nanorod Diffusion in Polymer Nanocomposites by Molecular Dynamics Simulations

Nanorod diffusion and polymer dynamics in nanocomposites were investigated by means of molecular dynamics simulations. We show that thin nanorods (spherocylinders) can diffuse much faster than that predicted by a Stokes–Einstein continuum model, similar to experiments, in the dilute nanorod regime. In entangled polymer matrices, nanorod diffusion reaches a plateau region. Increase of the nanorod diameter or aspect ratio (AR) slows its diffusion. The nanorod diffusion, at long time scales, displays a non-Gaussian behavior as is depicted by the several Gaussian peaks present in the self-part of the van Hove function. We also show that the unentangled polymer dynamics decreases in the nanocomposite due to the nanorods interfacial area.

Half-Encapsulated Au Nanorods@CeO2 Core@Shell Nanostructures for Near-Infrared Plasmon-Enhanced Catalysis

The technology of surface plasmon resonance (SPR) is considered to be highly attractive approach to directly harvest optical energy for photocatalytic reactions. However, photocatalytic application is limited mainly by inefficient absorption of catalysts in the visible and infrared range. In this work, an anisotropic Au@CeO2 mushroom-like core@shell nanostructure is designed by controlled hydrolysis of the cerium acetate utilizing the cetyltrimethylammonium bromide (CTAB) as a soft template. Special aspect ratio of the Au nanorods (Au NRs) and the anisotropy of the nanostructures increase the plasmon absorption in the frequency near-infrared range (NIR). Upon 808 nm laser illumination for 7 min, the temperature of the solution containing 75 ppm half-encapsulated Au NRs@CeO2 (h-Au@CeO2) increases up to 53.8 °C. Besides exhibiting plasmon-enhanced photothermal properties, h-Au@CeO2 also has good 4-nitrophenol (4-NP) catalytic reduction activity under near-infrared laser. The anisotropy of h-Au@CeO2 promotes...

Effects of Hydrostatic Pressure on the Surface Plasmon Resonance of Gold Nanocrystals.

The surface plasmon resonances of gold nanospheres and nanorods have been measured as a function of hydrostatic pressure up to 17 GPa in methanol-ethanol 4:1 solvent and up to 10 GPa in paraffin. Both the sphere resonance and the longitudinal rod resonance exhibit redshifts, whereas the transverse rod mode shows an extremely weak redshift or blueshift depending on the nanorod aspect ratio. Solidification of the solvent around 11 GPa causes some aggregation of the particles, readily identified through broadening of the surface plasmon band and further redshifting. Spectra collected during loading and unloading cycles exhibit only minimal hysteresis if the pressure remains below 11 GPa. The surface plasmon shifts are the result of two competing effects. Compression of the conduction electrons in the metals increases the bulk plasma frequency, which causes a blueshift. However, the increase in the solvent density under hydrostatic load leads to an increase in the solvent refractive index, which in turn leads to a redshift. We find that after accounting for the solvent contribution, we can spectroscopically determine the bulk modulus of the gold nanoparticles with a precision of 10%. The value obtained of K0 = 190 GPa is significantly higher than the value for bulk gold (167 GPa). Furthermore, we show that pressure-induced solidification causes a significant broadening and anomalous shift of the surface plasmon band that we attribute to aggregation and nanorod deformation.

Controllable synthesis of transparent dispersions of monodisperse anatase-TiO2 nanoparticles and nanorods

Controllable synthesis of monodisperse nanocrystals is still a great challenge. In this study, the control strategy of alcohol medium was developed to conveniently synthesize monodisperse anatase-TiO2 nanocrystals with controllable size and shape by sol-gel method combined with solvothermal treatment. The effects of the amount of stearic acid and water, and molecular structure of alcohol on the size, the shape and the dispersity of TiO2 nanocrystals were explored. The optimum synthesis conditions were achieved. Monodisperse TiO2 nanoparticles and nanorods were obtained by using linear and branched alcohols, respectively. The size of nanoparticles decreased from 12 to 5 nm with increasing carbon number of linear alcohol. The aspect ratio of nanorods was adjusted from 1 to 5 by selecting alcohols with different locations of branched methyl group. The as-prepared monodisperse TiO2 nanocrystals could be readily dispersed in some commonly-used solvents to form transparent nanodispersions. Furthermore, a possible formation mechanism was also investigated.

Design and efficient fabrication of micro-sized clusters of hydroxyapatite nanorods for dental resin composites

Dental resin-based composites have been used for more than 50 years. The size and the structure of inorganic filler have a great effect on the mechanical properties of the composite resin. In this study, novel micro-sized clusters of hydroxyapatite nanorods (MCHN) were designed and conveniently fabricated by spray drying combined with heat treatment. The effects of the aspect ratio of primary hydroxyapatite nanorods (HN), suspension concentration for spray drying and heat treatment temperature were explored. The results indicated that HN with a lower aspect ratio of 2 (HN-2) and a heat treatment temperature of 500 °C were beneficial to the construction of high-performance MCHN (MCHN-2). As compared to HN-2, MCHN-2 had a further increased filling amount by 10%. More importantly, the flexural strength, flexural modulus and compressive strength of the composite resin were greatly improved by 36.3%, 11.4% and 56.6%, respectively. Therefore, it could be envisioned that MCHN could have a great potential in dental restorative application.

Shape design of supported Au nanorods through morphological evolution: Coalescence, instability, reshaping

The morphological evolution of surface supported Au nanorods, induced by thermal heating, has been examined. This study is focused on the establishment of the connection of the nanorods morphology to the annealing temperature, on the elucidation of the acting microscopic mechanisms and quantitative evaluation of the involved parameters leading to the morphology evolution.In particular, after depositing the nanorods on SiO2 surface, thermal processes were performed to induce their morphological evolution and we pointed out our attention on:a)the study of the morphological evolution of single isolated Au nanorods, which was identified as a reshaping process towards a spherical shape. The morphological analysis led us to establish the correlation between the annealing temperature and the nanorods aspect ratio and to elucidate the basic atomic driving mechanism for the reshaping process;b)the study of the morphological evolution of closely spaced nanorods (forming a film over the substrate surface). The analysis led us to the identification of the mechanisms governing the nanorods joining and evolution in larger architectures which, then, operate a reshaping process.On the basis of the results, we set a general framework for the design of complex morphology nanostructures on surfaces with desired shape and aspect ratio.

Synthesis of ultra-narrow PbTe nanorods with extremely strong quantum confinement

Monodisperse, high-quality, ultra-narrow PbTe nanorods were synthesized for the first time in a one-pot, hot-injection reaction using trans-2-decenoic acid as the agents for lead precursors and tris(diethylamino)phosphine telluride together with free tris(diethylamino)phosphine as the telluride precursors. High monomer reactivity, rapid nucleation and fast growth rate derived from the new precursors led to the anisotropic growth of PbTe nanocrystals at low reaction temperatures (<150 °C). In addition, the aspect ratio of PbTe nanorods could be largely adjusted from 4 to 15 by tuning the Pb to Te precursor molar ratio and reaction temperatures. Moreover, the synthesized ultra-narrow PbTe nanorods exhibited extremely strong quantum confinement and presented unique optical properties. We revealed that the diameter and length of PbTe nanorods could significantly affect their optical properties, which potentially offer them new opportunities in the application of optoelectronic and thermoelectric devices and make them desired subjects for multiple exciton generation and other fundamental physics studies.

Multi-hierarchical profiling the structure-activity relationships of engineered nanomaterials at nano-bio interfaces

Increasing concerns over the possible risks of nanotechnology necessitates breakthroughs in structure–activity relationship (SAR) analyses of engineered nanomaterials (ENMs) at nano-bio interfaces. However, current nano-SARs are often based on univariate assessments and fail to provide tiered views on ENM-induced bio-effects. Here we report a multi-hierarchical nano-SAR assessment for a representative ENM, Fe2O3, by metabolomics and proteomics analyses. The established nano-SAR profile allows the visualizing of the contributions of seven basic properties of Fe2O3 to its diverse bio-effects. For instance, although surface reactivity is responsible for Fe2O3-induced cell migration, the inflammatory effects of Fe2O3 are determined by aspect ratio (nanorods) or surface reactivity (nanoplates). These nano-SARs are examined in THP-1 cells and animal lungs, which allow us to decipher the detailed mechanisms including NLRP3 inflammasome pathway and monocyte chemoattractant protein-1-dependent signaling. This study provides more insights for nano-SARs, and may facilitate the tailored design of ENMs to render them desired bio-effects.

Elastic deformations in semi-dilute Ni nanorod/hydrogel composites

Magnetic nanocomposites were prepared by dispersing uniaxial ferromagnetic Ni nanorods in poly(acrylamide) hydrogels. Field alignment of the nanorods during polymerization resulted in a magnetic texture which was explored for field-induced deformations in the elastic composite. At very low particle volume fraction $$<10^{-6}$$ , the magnetic torque resulted in a local rotation of the nanorods, measured by optical transmission of linearly polarized light, with a field- and orientation dependence in agreement with the Stoner–Wohlfarth model. The local rotation was virtually unaffected by an increase in the volume fraction to $$\sim 10^{-4}$$ which suggested negligible interparticle interactions or mutual compensation of opposing contributions. Elastic interactions, mediated by the deformation of the matrix, were investigated by FEM simulations for nanorods of different aspect ratio and relative spatial positions. Complementary experiments were performed by measuring the rotation of individual nanorods using laser scanning confocal microscopy. The results suggest interparticle interactions to be negligible in textured nanorod composites up to a volume fraction of $$10^{-4}$$ . Macroscopic deformations of Ni nanorod/hydrogel magnetic actuators in this concentration regime are expected to be solely determined by the intrinsic properties of the nanorods which was demonstrated using the example of a torsion cylinder.

Ultrahigh supercapacitance in cobalt oxide nanorod film grown by oblique angle deposition technique

Nanorod films of cobalt oxide (Co3O4) have been grown by a unique oblique angle deposition (OAD) technique in an e-beam evaporator for supercapacitor electrode applications. This technique offers a non-chemical route to achieve large aspect ratio nanorods. The fabricated electrodes at OAD 80° exhibited a specific capacitance of 2875 F/g. The electrochemically active surface area was 1397 cm−2, estimated from the non-Faradaic capacitive current region. Peak energy and power densities obtained for Co3O4 nanorods were 57.7 Wh/Kg and 9.5 kW/kg, respectively. The Co3O4 nanorod electrode showed a good endurance of 2000 charge-discharge cycles with 62% retention. The OAD approach for fabricating supercapacitor nanostructured electrodes can be exploited for the fabrication of a broad range of metal oxide materials.