Nanoscale Rods Research Articles

Rapid Shape Change and Spallation of Isolated Nanoscale Aluminum Cubes, Rods, Pyramids, and Spheres: Implications for Plasmonic and Energetic Materials

Rapid Shape Change and Spallation of Isolated Nanoscale Aluminum Cubes, Rods, Pyramids, and Spheres: Implications for Plasmonic and Energetic Materials

Oxidation behavior and mechanism of Al4O4C powders at 1000–1300 °C

The high temperature non–isothermal and isothermal oxidation behavior of Al4O4C powders were investigated in the temperature range of 1000 to 1300 °C. The phase composition, micro–structure evolution, and the thickness of the oxide scale were characterized. The Al4O4C powders showed a good oxidation resistance at 1000 and 1100 °C, owing to the generation of the dense nanoscale rod–like and worm–like α–Al2O3 layer. Density functional theory (DFT) calculation illustrated that Al4O4C performed a high–temperature stability due to the strong covalent bond. The grain sizes of α–Al2O3 increased evidently at 1200 °C, and the staggered growth of α–Al2O3 particles and their corresponding volume shrinkage dominated the generation of the porous surface structure of oxidized Al4O4C powders. Subsequently, the gas phase diffused quickly through these porous structures, and thus resulted in rapid and complete oxidation of Al4O4C powders at 1300 °C. The isothermal oxidation kinetics of Al4O4C powders can be accurately described by the Carter model, and their corresponding apparent activation energy was calculated to be 350.93 kJ/mol at 1000–1300 °C.

DNA double helix, a tiny electromotor.

Flowing fluid past chiral objects has been used for centuries to power rotary motion in man-made machines. By contrast, rotary motion in nanoscale biological or chemical systems is produced by biasing Brownian motion through cyclic chemical reactions. Here we show that a chiral biological molecule, a DNA or RNA duplex rotates unidirectionally at billions of revolutions per minute when an electric field is applied along the duplex, with the rotation direction being determined by the chirality of the duplex. The rotation is found to be powered by the drag force of the electro-osmotic flow, realizing the operating principle of a macroscopic turbine at the nanoscale. The resulting torques are sufficient to power rotation of nanoscale beads and rods, offering an engineering principle for constructing nanoscale systems powered by electric field.

Compound influence of surface and flexoelectric effects on static bending response of hybrid composite nanorod

Nanoscale beams and rods are extensively used in several nano-electro-mechanical systems (NEMS) and their applications such as sensors and actuators. The surface and flexoelectricity phenomena have an extensive effect on nanosized structures and are related to their scale-dependent characteristics. This article presents the effect of different surface parameters and flexoelectricity on the electrostatic response of graphene-reinforced hybrid composite (GRHC) nanorods (NRs) using the theory of linear piezoelectricity, Euler-Bernoulli (EB), and Galerkin residual method. Based on these theories, the theoretical and finite element (FE) model is produced to investigate the static bending deflection of GRHC NRs when subjected to point and uniformly distributed load (UDL) considering different boundary conditions: cantilever (FC), fixed-fixed (FF), and simply supported (SS). This proposed FE model provides a useful tool for analyzing and investigating the outcomes of analytical models, which are found to be in good agreement. Our results presented in this article reveal that the effect of surface and flexoelectricity on the static bending response of GRHC NRs is noteworthy. These effects diminish with increased thickness/diameter of NR, and hence, these effects can be neglected for large-sized structures. The results presented here would help to identify the desired electrostatic response of GRHC NRs in terms of static bending response for a range of NEMS using different loading and boundary conditions as well as graphene volume fraction. This current study offers pathways for developing new proficient novel GRHC materials with enhanced control authority and present models can be exploited for numerous other materials as well as line-type structural systems such as beams, wires, rods, column/piers, and piles to study their global response.

Advances of Hydroxyapatite Hybrid Organic Composite Used as Drug or Protein Carriers for Biomedical Applications: A Review

Hydroxyapatite (HA), especially in the form of HA nanoparticles (HANPs), has excellent bioactivity, biodegradability, and osteoconductivity and therefore has been widely used as a template or additives for drug delivery in clinical applications, such as dentistry and orthopedic repair. Due to the atomically anisotropic distribution on the preferred growth of HA crystals, especially the nanoscale rod-/whisker-like morphology, HA can generally be a good candidate for carrying a variety of substances. HA is biocompatible and suitable for medical applications, but most drugs carried by HANPs have an initial burst release. In the adsorption mechanism of HA as a carrier, specific surface area, pore size, and porosity are important factors that mainly affect the adsorption and release amounts. At present, many studies have developed HA as a drug carrier with targeted effect, porous structure, and high porosity. This review mainly discusses the influence of HA structures as a carrier on the adsorption and release of active molecules. It then focuses on the benefits and effects of different types of polymer-HA composites to re-examine the proteins/drugs carry and release behavior and related potential clinical applications. This literature survey can be divided into three main parts: 1. interaction and adsorption mechanism of HA and drugs; 2. advantages and application fields of HA/organic composites; 3. loading and drug release behavior of multifunctional HA composites in different environments. This work also presents the latest development and future prospects of HA as a drug carrier.

Photoreductive synthesis of nanoscale zero-valent iron rod assisted by phosphotungstic acid over graphite carbon nitride and its enhanced removal of Cr(VI) from water

Hexavalent chromium Cr(VI) as a virulent carcinogen has led to environmental pollution and health threats. Nanoscale zero-valent iron (NZVI) is considered one of the most effective environmental remediation materials in the field. NZVI/phosphotungstic acid/graphite carbon nitride (NZVI@HPW/g-C3N4) composites were facilely fabricated by photoreduction of ferrous irons on g-C3N4 flakes with the assistance of phosphotungstic acid. The TEM, SEM-EDS, XRD, FTIR, BET, and XPS analyses were conducted to explore the surface morphology and mechanism of the composites. NZVI0.9@HPW/g-C3N4 was chosen as the optimal composite forremoving Cr(VI) from water. The kinetics and thermodynamics experiments showed that the adsorption of Cr(VI) fitted well with the pseudo-second-order kinetic model and the Langmuir isothermal model. The maximum adsorption capacity of the adsorbents was 164.81 mg/g. Results demonstrated that adsorption of Cr(VI) was a principal process via a redox reaction in which zero-valent iron was oxidized and Cr(VI) species was reduced to Cr(III). Furthermore, NZVI0.9@HPW/g-C3N4 exhibited superior photocatalytic ability under visible light irradiation, which was 8.5 times higher than HPW/g-C3N4 and 15 times higher than g-C3N4. This work will provide a promising prospect for the dual utilization of light in wastewater remediation.

On longitudinal and transversal diffusion of carbon nanotubes

In this work, the anisotropy of diffusion of carbon nanotubes in water was studied by the molecular dynamics method. Two models of nanotubes were used, their lengths varied from 4 to 31 nanometers. The first model is a nanotube with armchair chirality, the second is connected solid nanoscale rods. The behavior of various components of the velocity autocorrelation function of the nanotubes center of mass has been studied. It was established that the transverse component of this function has a negative region and a minimum point, in contrast to the average autocorrelation function, which decays monotonically. It is shown that the diffusion coefficients in the longitudinal and transverse directions can differ several times; the method proposed in this work was used to determine them. The effect of anisotropy increases with an increase in the ratio of the characteristic sizes of the nanotube. Using the Stokes - Einstein formula, the effective hydrodynamic radii of nanotubes have been determined. In all cases, the effective radius is significantly less than the tube length.

Scale-dependent torsional vibration response of non-circular nanoscale auxetic rods

In the current paper, analysis of torsional vibration behavior of non-circular nanorods made of auxetic honeycomb material is investigated for the first time. The triangular and elliptical cross-sections are selected to be analyzed. Moreover, one of the distinct properties of auxetic honeycomb materials is that they possess a negative Poisson’s ratio, which can be effective on the design and analysis of structures. In order to capture a small size or scale effect, the constitutive relation of nanorods is modified based on Eringen’s nonlocal elasticity theory (ENET). Hamilton’s principle is employed to obtain the kinematic relation of nanoscale rods. The nonlocal derived governing equations of non-circular auxetic nanorods are solved by utilizing an analytical method with respect to different boundary conditions. In order to verify the correctness of obtained outcomes, the results are compared to previous investigations, and good agreement can be observable. The influences of various parameters such as both Clamped–Clamped (C–C) and Clamped-Free (C-F) boundary conditions, nonlocal parameters, inclined angles, and geometrical ratios are explored and illustrated in the framework of several figures, which can be seen in detail.

Localized Surface Plasmon Fields Manipulation on Nanostructures Using Wavelength Shifting

Metallic nanowires have been utilized as a platform for propagating surface plasmon (SPs) fields. To be exploited for applications such as plasmonic circuits, manipulation of localized field propagating pattern is also important. In this study, we calculated the field distributions of localized surface plasmons (LSPs) on the specifically shaped nanostructures and explored the feasibility of manipulating LSP fields. Specifically, plasmonic fields were calculated at different wavelengths for a nanoscale rod array (I-shaped), an array connected with two nanoscale rods at right angles (T-shaped), and an array with three nanoscale rods at 120° to each other (Y-shaped). Three different types of nanostructures are suggested to manipulate the positions of LSP fields collaborating with adjustment of wavelength, polarization, and incident orientation of light source. The results of this study are important not only for the understanding of the wavelength-dependent surface plasmon field localization mechanism but also for the applicability of swept source-based plasmonic techniques or designing a plasmonic circuit.

Probability-Dependent Precipitation Strengthening Effect of Anisotropic Precipitate in Al-Mg-Si Alloy Produced by T6 Heat Treatment

This study proposed a constitutive equation to predict the change in yield strength according to the behavior of β″ metastable precipitates, which have a profound effect on strength among materials precipitated during the T6 heat treatment of Al-Mg-Si alloy. The β″ precipitate is a metastable phase before it becomes a β (Mg2Si) precipitate, and is distributed in the form of nano-scale rods in the aluminum alloy matrix. Existing precipitation strengthening models assume the shape of the precipitate to be spherical, and in that case the equation that depends on the Orowan mechanism with the average precipitate size and distribution should dominate. However, precipitates are formed in various shapes and sizes by anisotropic growth. In particular, rod-shaped precipitates are not suitable for the existing precipitation strengthening model. In this study, an Al-Mg-Si alloy was fabricated by gravity casting followed by T6 heat treatment. The new precipitation strengthening effect equation proposes that the β″ precipitate affects yield strength during plastic deformation of the Al-Mg-Si alloy. The proposed precipitation strengthening effect equation probabilistically considers the Critical Resolved Shear Stress (CRSS), which varies depending on the angle between the dislocation and the precipitate, when the dislocation passes through a rod-shaped precipitate.

Self-Assembly of 2D Nematic and Random Arrays of Sterically Stabilized Nanoscale Rods with and without Evaporation.

The adequate manipulation of nanometer-scale building blocks using dispersion systems is regarded as a fundamental technique to fabricate elaborate microstructures. Although a liquid flow with evaporation is generally regarded as an essential factor for the self-assembly of floating blocks, experimental evidence has not been sufficient to clarify the importance of the flow in the dispersion systems. In the present study, 2D nematic layers of sterically stabilized nanoscale calcite rods were achieved in a millimeter-scale region on a solid substrate via the very slow recession of an organic dispersion with evaporation. 2D random arrays of the nanorods were obtained via recession of the liquid in the same system without evaporation. When the nanorods were not sterically stabilized, 3D random arrays were formed even with evaporation. We demonstrated that the evaporation-driven flow of sterically stabilized nanorods to a confined space at the air-liquid-solid interface is essential for the formation of 2D nematic structures on a substrate.

Effective removal of methylene blue using nanoscale manganese oxide rods and spheres derived from different precursors of manganese

Nanoscale manganese oxide with different morphologies were developed at room temperature using different precursor salts (potassium permanganate and manganese sulfate). The obtained nanoscale morphologies, i.e., rod and sphere-shaped were characterized using BET surface area analyzer, SEM, TEM, and XRD. The manganese oxide possessed the rod and sphere-like morphologies with different pore structures. The adsorption of methylene blue on mesoporous manganese oxide followed the pseudo-second-order kinetics and best fitted with the Freundlich adsorption isotherm model with a removal capacity of 2914 mg g−1. The effect of irradiation time on degradation efficiency was also examined, which followed the first-order kinetics with a degradation efficiency of 93.12%. Furthermore, the recycling studies revealed that the spherical manganese oxide retained over 90% of the photodegradation efficiency after three cycles of methylene blue degradation, which proves its stability for practical applications. Therefore, mesoporous manganese oxide with significant adsorption and remarkable photodegradation capability can provide a way forward to fine-tune the material's properties for effective environmental remediation.

Valorization of khat (Catha edulis) waste for the production of cellulose fibers and nanocrystals.

Cellulose fibers (C40 and C80) were extracted from khat (Catha edulis) waste (KW) with chlorine-free process using 40% formic acid/40% acetic acid (C40), and 80% formic acid/80% acetic acid (C80) at the pretreatment stage, followed by further delignification and bleaching stages. Cellulose nanocrystals (CNCs40 and CNCs80) were then isolated from C40 and C80 with sulfuric acid hydrolysis, respectively. Thus, the current study aims to isolate cellulose fibers and CNCs from KW as alternative source. The KW, cellulose fibers, and CNCs were investigated for yield, chemical composition, functionality, crystallinity, morphology, and thermal stability. CNCs were also evaluated for colloidal stability, particle size, and their influence on in vitro diclofenac sodium release from gel formulations preliminarily. The FTIR spectra analysis showed the removal of most hemicellulose and lignin from the cellulose fibers. The XRD results indicated that chemical pretreatments and acid hydrolysis significantly increased the crystallinity of cellulose fibers and CNCs. The cellulose fibers and CNCs exhibited Cellulose Iβ crystalline lattice. TEM analysis revealed formation of needle-shaped nanoscale rods (length: 101.55–162.96 nm; aspect ratio: 12.84–22.73). The hydrodynamic size, polydispersity index, and zeta potential of the CNCS ranged from 222.8–362.8 nm; 0.297–0.461, and -45.7 to -75.3 mV, respectively. CNCs40 exhibited superior properties to CNCs80 in terms of aspect ratio, and colloidal and thermal stability. Gel formulations containing high proportion of CNCs sustained diclofenac sodium release (< 50%/cm2) over 12 h. This study suggests that cellulose fibers and nanocrystals can be successfully obtained from abundant and unexploited source, KW for value-added industrial applications.

Substrate free Defect-rich one dimensional ZnO nanostructures

One dimensional (1-D) nanostructures of ZnO have been grown using modified ultrasonic-assisted hydrothermal method at low temperature (95οC) in order to investigate its structural, optical and photoluminescence properties. Zinc nitrate and HMT acts as a source of zinc ions (Zn2+) and hydroxide ions (OH−) respectively for the growth of ZnO nanostructures. 1-D ZnO nanostructures consist of well-defined hexagonal shaped nanoscale rods and tubes-like morphologies. The X-ray diffraction pattern confirms the formation of hexagonal wurtzite phase of ZnO with good crystallinity. The crystallite size corresponding to major peaks lies between 39 and 44 nm. The crystallinity corresponding to (0 0 2) plane is found to be 2.061. The optical band gap is found to be 3.42 eV. Room temperature photoluminescence spectrum of 1-D ZnO nanostructures revealed the existence of high concentration of defect emissions i.e. violet, blue-green, green and yellow emissions.

Molecular Origin of Electrical Conductivity in Gold-Polythiophene Hybrid Particle Films.

Hybrid electronic materials combine inorganic metals and semiconductors with π-conjugated polymers. The orientation of the polymer molecules in relation to the inorganic components is crucial for electrical material properties and device performance, but little is known of the configuration of π-conjugated polymers that bind to inorganic surfaces. Highly curved surfaces are common when using nanoscale components, for example, metal nanocrystal cores covered with conductive polymers. It is important to understand their effect on molecular arrangement. Here, we compare the molecular structures and electrical conductivities of well-defined nanoscale gold spheres and rods with shells of the covalently bound polythiophene PTEBS (poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate]). We prepared aqueous sinter-free inks from the particles and printed them. The particles formed highly conductive films immediately after drying. Films with spherical metal cores consistently had 40% lower conductivities than films based on nanorods. Raman and X-ray photoelectron spectroscopy revealed differences in the gold-sulfur bonds of PTEBS on rods and spheres. The fractions of bond sulfur groups implied differences in the alignment of PTEBS with the surface. More polymer molecules were bound in an edge-on configuration on spheres than on rods, where almost all polymers aligned "face-on" with the metal surface. This leads to different interface resistances: gold-polythiophene-gold interfaces between rods with π-π-tacked face-on PTEBS apparently foster electron transport along the surface-normal direction, while edge-on PTEBS does not. Molecular confinement thus increases the conductivity of hybrid inks based on highly curved nanostructures.

Shearing with solvent vapor annealing on block copolymer thin films for templates with macroscopically aligned nanodomains

A template with macroscopically aligned nanopatterns can be an effective vehicle for arranging nanoscale particles or rods in a particular orientation to achieve their anisotropic properties. A room-temperature process is also desirable for nanoscale patterning of heat-sensitive functional molecules such as organic fluorophores. Here, large-area orientation of nanodomains of block copolymers is demonstrated by simultaneous shearing and solvent vapor annealing at room temperature. The shear-aligned nanodomains are applied to a chemical template for nanoscale patterning of green fluorescent molecules. In addition, the grooved nanochannels obtained from the macroscopically aligned nanodomains work as a physical template for guiding Au nanorods to end-to-end assemblies which exhibit the polarization-dependent plasmonic extinction.

Improving the optical properties of organic light-emitting diodes using random nanoscale rods with a double refractive index

In this study, random nanoscale rods (RNRs) with a double refractive index were fabricated via spin coating, dry etching, and sputtering, which are processes that are extensively applied in industry. With regard to optical properties, the RNRs with a double refractive index (RNRsD) exhibited a total transmittance that was >90% in the visible range and an optical haze in the range of 42%–50% at a wavelength of 520 nm. Organic light-emitting diodes (OLEDs) with RNRsD, where SiO2 was deposited on the RNRs via radiofrequency sputtering, exhibited an enhancement of 34.5% in the external quantum efficiency compared with OLEDs with the bare substrate. Furthermore, the color variation of the OLEDs with the optimal RNRsD with respect to a change in the viewing angle was improved from color coordinates of Δ(x, y) = (0.032, 0.034) to Δ(x, y) = (0.014, 0.014). Therefore, the proposed film can be used as a scattering layer for enhancing the light extraction and viewing angle of OLEDs by reducing the substrate mode light loss and changing the direction of light. In addition to using a low-temperature fabrication process that does not employ a photomask and a lithographic template, the proposed method is applicable to flexible devices because it uses a polymer and a thin inorganic film.

High Performance of Low‐Temperature‐Cofired Ceramic with Al2O3/BN Biphasic Ceramics Based on B2O3–Bi2O3–SiO2–ZnO Glass

With the rapid development of microelectronic information technology, high‐power electronic devices require high heat dissipation. Herein, the preparation of low‐temperature cofired ceramic (LTCC) applications with excellent thermal conductivity and dielectric properties is focused. B2O3–Bi2O3–SiO2–ZnO (BBSZ) glass/Al2O3/BN green sheets are prepared by tape casting and sintered at 850 °C. The crystal phase composition, microstructure, thermal conductivity, thermal expansion coefficient, and dielectric properties of LTCC are investigated. It is shown that nanoscale rod crystals ZnAl2O4 and Bi are formed in the composite. The generated nanoscale rod crystals build a 3D heat conduction channel in the composite. The thermal conductivity of the sintered sheet with 20 wt% BN is 5.165 W m−1 K−1. The sintered sheet containing 20 wt% BN has a low coefficient of thermal expansion (2.92 ppm °C−1) matched well with silicon and excellent dielectric properties (εr = 3.9672, tan δ = 1.49 × 10−3) at 20 GHz. This material has great potential applications in electronic devices.

Free axial vibration of cracked axially functionally graded nanoscale rods incorporating surface effect

This work aims to study effects of the crack and the surface energy on the free longitudinal vibration of axially functionally graded nanorods. The surface energy parameters considered are the surface stress, the surface density, and the surface Lame constants. The cracked nanorod is modelled by dividing it into two parts connected by a linear spring in which its stiffness is related to the crack severity. The surface and bulk material properties are considered to vary in the length direction according to the power law distribution. Hamilton\'s principle is implemented to derive the governing equation of motion and boundary conditions. Considering the surface stress causes that the derived governing equation of motion becomes non-homogeneous while this was not the case in works that only the surface density and the surface Lame constants were considered. To extract the frequencies of nanorod, firstly the non-homogeneous governing equation is converted to a homogeneous one using an appropriate change of variable, and then for clamped-clamped and clamped-free boundary conditions the governing equation is solved using the harmonic differential quadrature method. Since the present work considers effects of all the surface energy parameters, it can be claimed that this is a comprehensive work in this regard.

Plasma waves in limited size media

In this work, an analytical derivation is applied to study electronic plasma waves in limited size plasma and a generalized formula for oscillation frequency of plasma wave is obtained in this case. The effect of thermal motion of electrons is considered and the ions are considered to be rigid. In limited size plasma the wave vector of plasma waves has discrete values and this causes the oscillation frequency to have different values proportional to the electron positions. Also, this theory is expanded for the case that a constant electric field is applied to the media and group velocity is studied for finite and infinite plasmas. This model is expanded for metal particles as micro and nano-scale rods and particles and also typical Cs plasma embedded in microns. The effect of particle size on the value of oscillation frequencies is studied and micro and nano-scale metal particles are compared. It could open new sights into properties of micro and nano-rods and nano-particles, two dimensional materials and also quark–gluon plasma physics.