Short Nanorods Research Articles

Short Gold Nanorod Growth Revisited: The Critical Role of the Bromide Counterion

A one-step, surfactant-assisted, seed-mediated method has been utilized for the growth of short gold nanorods with reasonable yield by modifying an established synthesis protocol. Among the various parameters that influence nanorod growth, the impact of the bromide counterion has been closely scrutinized. During this study it has been shown that, irrespective of its origin, the bromide counterion [cetyltrimethylammonium bromide (CTAB) or NaBr] plays a crucial role in the formation of nanorods in the sense that there is a critical [Br(-)]/[Au(3+)] ratio (around 200) to achieve nanorods with a maximum aspect ratio. Beyond this value, bromide can be considered as a poisoning agent unless shorter nanorods are required. The use of AgNO(3) helps in symmetry breaking for gold nanorod growth, whereas the bromide counterion controls the growth kinetics by selective adsorption on the facets of the growth direction. Thus, a proper balance between bromide ions and gold cations is also one of the necessary parameters for controlling the size of the gold nanorods; this has been discussed thoroughly. The results have been discussed based on their absorption spectra and finally shape evolution has been confirmed by TEM. Due to their efficient absorption in the near-IR region, these short nanorods were used in photothermal imaging of living COS-7 cells with improved signal-to-background ratios.

Oriented Assembly of Gold Nanorods on the Single‐Particle Level

AbstractNon‐spherical colloidal nanoparticles have great potential for applications owing to their enhanced directional properties. However, the lack of methods to precisely assemble them on surfaces has hindered exploitation of their properties for planar devices. Here, the oriented assembly of short gold nanorods with lengths below 100 nm from colloidal suspensions is demonstrated. A locally induced phase transition confines the colloidal nanorods at a receding three‐phase contact line that is controllably moved over a nanostructured surface in a capillary assembly process. Dedicated topographical trapping sites allow for aligned assembly of the nanorods on the single‐particle level. The feasibility of this method is demonstrated by assembling nanorods into long‐range‐ordered, non‐close packed arrays that could serve as anti‐counterfeit labels by virtue of their distinct optical appearance in the far‐field. Furthermore, oriented nanorod dimers that are deterministically assembled have the potential to function as nano‐plasmonic antenna devices.

Microwave-assisted synthesis of CePO4 nanorod phosphor with violet emission

Monoclinic and hexagonal CePO4 nanoparticles and nanorods were successfully synthesized from Ce(NO3)3·6H2O and Na3PO4·12H2O solutions at pH 1–5 by a 180 W microwave radiation for 60 min. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). XRD patterns revealed that the products are hexagonal CePO4 structures at pH 2–5, and monoclinic CePO4 structures at pH 1. SEM characterization shows that these products were nanoparticles, short nanorods, and long nanorods, controlled by the pH of the precursor solutions. Optical properties of the nanorods were also investigated by ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopy.

Hydrothermal Synthesis and Electrochromic Properties of Potassium Tungsten Oxide Nanorods

Hexagonal K2W4O13 nanorods have been synthesized by hydrothermal treatment of the WO3 x H2O precipitate at 180 degrees C in the presence of K2SO4. The K2W4O13 nanorod single crystals of approximately 12 nm in diameter and tens to few hundreds nm long with the principal axis along the (001) direction were obtained when hydrothermal treatment was conducted in the presence of sufficient amount of K2SO4 while shorter nanorods with the same preferred orientation were obtained when less amount of K2SO4 was employed. On the other hand, square platelets of approximately 100 nm wide were obtained when prepared in the absence of the K2SO4. The important role of K2SO4 on morphological control of the hydrothermal products was explained based on selective adsorption of the sulfate ions on the crystal planes parallel to the (001) direction retarding the growth of these faces. The nanorod film showed satisfactory electrochromic property and can be used as a promising material in electrochromic application.

Effects of Anions on Nanostructuring of Cationic Amphiphilic Peptides

The effects of addition of a series of stoichiometric salts on the nanostructuring of cationic amphiphilic peptides have been investigated through the combination of atomic force microscopy (AFM), circular dichroism (CD), and turbidity measurements. The results revealed that anions had more pronounced effects than cations in tuning the nanostructures formed from these peptides. Addition of ClO(3)(-), NO(3)(-), and Br(-) could stabilize the primary nanostructures (nanostacks, nanospheres, or short nanorods) formed by A(9)K and I(3)K and effectively inhibit their growth into longer nanostructures (nanorods or nanotubes). In contrast, the anions of Cl(-), SO(4)(2-), HPO(4)(2-), PO(4)(3-), and C(6)H(5)O(7)(3-) (citrate) favored the axial growth of these peptides to form long intersecting nanofibrils and led to an increase in diameter and surface roughness, as well, clearly enhancing their propensity for nanostructuring. The efficiency of different anions in promoting the growth of peptide nanoaggregates into larger ones could be ordered as ClO(3)(-) < NO(3)(-) ≤ Br(-) < Cl(-) < SO(4)(2-) < HPO(4)(2-) < PO(4)(3-) < C(6)H(5)O(7)(3-), broadly consistent with the Hofmeister anion sequence. These observations were well rationalized by considering different aspects of direct interactions of the anions with the peptide molecules.

Ionic liquid-assisted synthesis, structural characterization, and photocatalytic performance of CdS nanocrystals

With the assistance of the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentylphosphinate), we have successfully synthesized short nanorods, quasi-nanospheres and faceted CdS nanoparticles via thermal decomposition of cadmium diethyldithiocarbamate complexes. It was shown that the shape, size and crystallinity of the products could be controlled through delicate regulation of the reaction temperature, monomer concentration, reaction time, and ionic liquid ratio. We found that higher temperature was beneficial to the good crystallinity, while the lower temperature and higher monomer concentration were in favor of anisotropic structures. The used ionic liquid contributed to the formation of hexagonal phase CdS nanocrystals, and its ratio played an important role in determining the ultimate morphology of products. The possible mechanism for the formation CdS nanocrystals was proposed. Furthermore, the as-prepared CdS samples demonstrated a highly photocatalytic activity in the degradation of methyl orange under visible light irradiation.

Investigation of Substrate Influence on Tin Dioxide Nanostructures Synthesized Using Horizontal Furnace

SnO2 nanostructures were directly synthesised by chemical vapour transport on different substrates in a horizontal furnace. The influence of substrate on the morphology of these nanostructures was investigated by changing the substrate type, coating, and temperature. The SnO2 nanowires and nanorods were one dimensional (1D) structures with widths and lengths of 50-200 nm and several micrometers respectively. Scanning electron microscope (SEM) images show formation of short nanorods with lengths of less than 1 microm on indium-tin oxide (ITO) substrates. The effect of substrate temperature on growth was studied. SnO2 nanowires were obtained using silicon substrate, and the effect of Au coating on the size and morphology of these structures was proposed. By coating the Si wafer with a thin layer of Au, the size of the nanostructure was reduced and the length increased. The differences in size and morphology are shown by transmission electron microscopy (TEM). X-ray diffraction (XRD) spectra show tetragonal structures for both substrates.

Fano resonances in active plasmonic resonators consisting of a nanorod dimer and a nano-emitter

The optical emission response of a single nano-emitter coupled with a plasmonic nanorod dimer is investigated, where the short and long nanorods in the dimer support dipolar and quadrupolar plasmon resonance, repsectively. Fano resonances are observed with a nano-emitter being placed at either apex of the dimer. However, no Fano resonance is seen when the nano-emitter is placed in the gap of the dimer. Bonding and antibonding dipolar-quadrupolar plasmon couplings are closely related to the Fano resonances in this dimer system.

Synthesis and characterization of La(OH) 3 nanopowders from hydrolysis of lanthanum carbide

The lanthanum carbide alloy was induction melted in vacuum induction melting furnace from lanthanum and graphite with the mass ratio of 89:11. Lanthanum hydroxide (La(OH) 3) nanopowders were prepared by a simple hydrolysis of lanthanum carbide at room temperature under normal atmospheric pressure without any surfactant. X-ray diffraction (XRD) showed that the nanoparticles were with a hexagonal structure. The effect factors such as reaction time, reaction temperature and the mass ratio of lanthanum carbide powders to H 2O on BET surface area of the obtained nanopowders were investigated. Furthermore, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) showed that nanopowders behaved the morphology of short nanorod. The longitudinal growth direction of the nanorod had an angle of about 14° with the (101) lattice plane and the lateral growth direction had an angle of about 35° with the (200) lattice plane. The mechanism of formation of nanorod was discussed on the basis of the experimental results.

Fano resonances in dipole-quadrupole plasmon coupling nanorod dimers

We theoretically investigate the plasmon coupling in metallic nanorod dimers. A pronounced dip is found in the extinction spectrum due to plasmonic Fano resonance, which is induced by destructive interference between the bright dipole plasmon of a short nanorod and the dark quadrupole plasmon of a long nanorod. This Fano interference can also be explained as the coupling between the bright and dark modes both supported by the whole dimer. The Fano resonance can be tuned by adjusting the spatial or spectral separation between two nanorods in the dimer.

The Effect of Substrate Temperature on the Spray-Deposited TiO&lt;SUB&gt;2&lt;/SUB&gt; Nanostructured Films for Dye-Sensitized Solar Cells

The nanostructured TiO2 films have deposited on SnO2:F (FTO) coated glass substrate by spray pyrolysis technique at different substrate temperatures of 200-500 degrees C. The structural, surface morphological and optical properties of TiO2 films significantly vary with the substrate temperature. The surface of the TiO2 films deposited at 400 degrees C shows the nanoflakes and short nanorods (approximately 130 nm) like structures while the TiO2 films prepared at 500 degrees C shows only the nanoflakes like structures. The band gap of the TiO2 films prepared at higher temperatures (300-500 degrees C) becomes narrow due to presence the rutile phases in their crystal structure. Ruthenium (II) complex as a dye, KI/I2 as an electrolyte and carbon on FTO glass as a counter electrode has used to fabricate the dye-sensitized solar cell (DSC). The TiO2 film deposited at 400 degrees C has showed the best photovoltaic performance in DSC with the efficiency of 3.81%, the photovoltage of 773 mV, the photocurrent of 8.34 mA/cm2, and the fill factor of 56.17%. The photovoltage of the DSC increases with the increase of substrate temperature during the deposition of TiO2 films. Moreover, all the DSCs exhibit reasonably high fill factor value.

Electrochemical Assemble of Single Crystalline Twin ZnO Nanorods

ZnO twin nanorods (TNs) have been successfully grown on F-doped SnO2 (FTO) glass by a simple electrochemical assemble process. The TNs were made up of two short nanorods via sharing the same crystallographic orientation along the (001) direction. The optical properties were investigated by UV-vis-NIR spectroscopy and photoluminescence (PL) spectrum. The resulting films had a strong UV absorption from 400 to 350 nm and the intensity of the green emission could be adjusted by changing the current density which might lead the ZnO TNs applicable as photosensitive materials. Moreover, the growth mechanism was studied and the probable electrochemical deposition formation process was proposed.

Synthesis and characterization of ruthenium dioxide nanostructures

We report the synthesis of ruthenium dioxide (RuO2) nanostructures by thermal evaporation of RuO2 powder. RuO2 nanostructures of different shapes were synthesized at various concentration, flow rate, and pressure of oxygen. At a constant pressure of 3 torr of flowing oxygen, polygonal prism-like RuO2 nanorods with flat tips were grown at an O2 flow rate of 100 sccm; club-shaped nanorods with obelisk tip were formed at 300 and 600 sccm, and hollow rods with square tip were formed at 1800 sccm. A mixture of O2 and Ar at a total flow rate of 600 sccm led to the formation of short club-shaped nanorods indicating the suppression effect of Ar on the growth of nanorods. The pressure also had a significant effect on the formation of RuO2 nanostructures, at a fixed flow rate of 600 sccm of O2, a pressure of 3 torr resulted in the growth of club-shaped RuO2 nanorods, while high pressures of 380 and 760 torr resulted in the formation of both linear club-shaped and pine tree-like hierarchical RuO2 nanorods. X-ray diffraction and transmission electron microscopy analysis indicated the formation of tetragonal phase of RuO2 with high crystallinity. A density functional calculation on RuO2, RuO3, and RuO4 was performed to help to explain the experimental results.

The effect of 1-N-alkyl chain of ionic liquids [Cnmim]+Br− (n = 2, 4, 6, 8) on the aspect ratio of ZnO nanorods: syntheses, morphology, forming mechanism, photoluminescence and recyclable photocatalytic activity

Using a pure ionic liquid-assisted solid-state-like synthesis method under 80 degrees C, high quality zinc oxide (ZnO) nanorods in 1-alkyl-3-methylimidazolium and bromide anions ionic liquids C(n)mimBr-+(-) (n = 2, 4, 6, 8) were realized. The size effect of the N-alkyl chains of ionic liquids hindered the further growth of ZnO nanorods and the aspect ratio (length/diameter, L/D) of ZnO nanorods (from 40 : 1, 20 : 1, 10 : 1, to 5 : 1) were realized by rationally tuning the length of the organic cation groups. Long octyl chains (9.93 angstrom) resulted in short ZnO nanorods (with L/D = 5 : 1), otherwise, short ethyl chains (2.53 angstrom) resulted in long ZnO nanorods (with L/D = 40 : 1). The growth mechanism of the above ZnO nanorods was mainly due to electrostatic interactions between cations of the ionic liquids and the ZnO crystal nucleus, causing the preferential growth on the 0001 directions of the hexagonal ZnO. The as-obtained short ZnO nanorods (with L/D = 5 : 1) exhibited defect-related green-yellow emission under UV excitation, and acted as effective recyclable photocatalysts during six photodegradation cycles of the organic dye molecule Rhodamine B, suggesting promising potential for environmental applications. This systematic study highlighted that the structures and morphology of ZnO nanomaterials could be controllable via specifically varying the molecular structure of 1-alkyl-3-methylimidazolium cation-based ionic liquids, and then with the tuned photocatalytic properties and optical and electronic functions of them.

Fabrication of single-crystalline ZnSe multipod-based structures

ZnSe multipod-based structures, including tetrapod-like microrods, long microwires, and short nanorods, are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst. The morphologies could be well controlled by simply adjusting the deposition position. The phase structures, morphologies, and optical properties of the products are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures. The presented route is expected to be applied to the synthesis of other II-VI groups or other group’s semiconductor materials with controllable morphologies.

Transition from Microscale-Faceted Structures to Ultra-Dense GaN Nanowires

ABSTRACTCreation of nanoscale building blocks with various sizes and shapes are critical for the progress of nanotechnology. The synthesis of GaN nanowires by chemical vapor deposition (CVD) using Ga and NH3 as source materials on SiO2/Si substrate was systematically studied. Various types of catalyst materials, including gold (film and nanoparticle), nickel (film and nanoparticle), silver, cobalt and iron, have been used. The growth runs have been carried out at temperatures between 800 and 1100oC under two different carrier gases; H2 and Ar. Initial growth runs using Ar as carrier gas resulted in microscale-faceted nanostructures and short nanorods regardless of the growth temperature or reactor pressure. We have successfully achieved ultra-dense interwoven long nanowires using hydrogen as carrier gas at 1100oC. In fact, the yield has been very high for both gold and nickel catalysts. It should be emphasized that combination of high-temperature and hydrogen has resulted in ultra-dense interwoven long GaN nanowires. These results suggest a radical change in growth kinetics at high temperatures in the presence of H2. The GaN nanowire diameters are in the range of 15 nm to 50 nm and lengths up to hundred microns. The grown nanowires have been characterized by scanning electron microscopy (SEM with EDS), atomic force microscopy (AFM), x-ray diffraction (XRD), and transmission electron microscopy (TEM).

Nanoscale semiconductor–insulator–metal core/shell heterostructures: facile synthesis and light emission

Controllably constructing hierarchical nanostructures with distinct components and designed architectures is an important theme of research in nanoscience, entailing novel but reliable approaches of bottom-up synthesis. Here, we report a facile method to reproducibly create semiconductor-insulator-metal core/shell nanostructures, which involves first coating uniform MgO shells onto metal oxide nanostructures in solution and then decorating them with Au nanoparticles. The semiconductor nanowire core can be almost any material and, herein, ZnO, SnO(2) and In(2)O(3) are used as examples. We also show that linear chains of short ZnO nanorods embedded in MgO nanotubes and porous MgO nanotubes can be obtained by taking advantage of the reduced thermal stability of the ZnO core. Furthermore, after MgO shell-coating and the appropriate annealing treatment, the intensity of the ZnO near-band-edge UV emission becomes much stronger, showing a 25-fold enhancement. The intensity ratio of the UV/visible emission can be increased further by decorating the surface of the ZnO/MgO nanowires with high-density plasmonic Au nanoparticles. These heterostructured semiconductor-insulator-metal nanowires with tailored morphologies and enhanced functionalities have great potential for use as nanoscale building blocks in photonic and electronic applications.

Facile Synthesis of Porous SnO2 Spherical-Like Aggregates and Their Gas Sensing Property

Porous spherical-like aggregates synthesis of SnO2 crystals was achieved via a hydrothermal process in the mixed solvents of water and ethanol. The products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman measurements. Morphological characterization showed that porous spherical-like aggregates were composed of short nanorods. Three main peaks broadening and shifting to high wavenumber in Raman spectrum implied that the components of the products had a smaller size. The result of the gas sensing measurement indicated that porous spherical-like aggregates had excellent ethanol gas sensing property compared to that of nanoparticles.

Morphology of NaNdF 4 nanocrystals from Nd(C 3H 7COO) 3·Phen and Nd(NO 3) 3·Phen (Phen, 1,10-phenanthroline) as neodymium precursors

A series of NaNdF 4 nanocrystals was synthesized via a facile hydrothermal route with Nd(C 3H 7COO) 3·Phen and Nd(NO 3) 3·Phen (Phen, 1,10-phenanthroline) as the Nd precursors. Distinct effect of the neutral donor ligand (Phen) on the morphology of NaNdF 4 nanocrystals was demonstrated. When Nd(C 3H 7COO) 3·Phen was chosen and the hydrothermal reaction temperature was controlled at 220 °C, the NaNdF 4 nanocrystals with uniform short nanorod shape were obtained. The sizes of the as-prepared nanorods could be tuned by changing the hydrothermal temperatures. This method provided a useful way for the preparation of sodium rare-earth fluoride nanocrystals with controlled shapes and sizes.

Anodic Deposition of Ultrathin TiO2 Film with Blocking Layer and Anchoring Layer for Dye-Sensitized Solar Cells

Ultrathin anatase TiO2 films were coated on the fluorine-doped tin oxide (FTO) glass by anodic electrodeposition followed by annealing at 450°C before the formation of thick TiO2 layer. The electrodeposited TiO2 films were more compact structure near the FTO surface (inner layer), and became less compact further away from the surface (outer layer). The outer layer of film deposited at 10 μA cm−2 was composed of granular nanoparticles and that of film deposited at 5 μA cm−2 was composed of short nanorods. The inner compact layer could act as a blocking layer to suppress the charge recombination. The outer loose layer could provide an anchoring layer for a better electrical contact between FTO and thick TiO2 layer. The photoelectron conversion efficiency (η) of dye-sensitized solar cell (DSC) using TiO2-coated FTO deposited at 10 μA cm−2 was 6.9%, which is higher than that of DSC using bare FTO (6.5%). The outer anchoring layer composed of short nanorods deposited at 5 μA cm−2 could significantly reduce the interfacial contact resistance between FTO and main TiO2 layer. Therefore, η of DSC was further increased to 7.1% after employing the TiO2-coated FTO deposited at 5 μA cm−2.