Defect-pit-assisted growth of GaN nanostructures: nanowires, nanorods and nanobelts

A new method using defect-pit-assisted growth technology to successfully synthesize the high-quality single crystalline GaN nanostructures by ammoniating Ga(2)O(3) films was proposed in this paper. During the ammoniating process, the amorphous middle buffer layer may unavoidably produce some defects and dislocations. Some defect pits come out, which have the lowest surface energy and can subsequently be used as a mask/template or act as potential nucleation sites to fabricate the GaN actinomorphic nanostructures. The as-prepared products are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results indicate that all the reflections of the samples can be indexed to the hexagonal GaN phase and the clear lattice fringes in HRTEM further confirm the growth of high-quality single-crystal GaN nanostructures. The SEM images show that the nanostructures have been realized under different experimental conditions exhibiting different shapes: nanowires, nanorods, and nanobelts. No particles or other nanostructures are found in the SEM study, demonstrating that the product possesses pure nanostructures. These nanostructures show a very good emission peak at 366 nm, which will have a good advantage for applications in laser devices using one-dimensional structures. Finally, the growth mechanism is also briefly discussed.     

Room temperature solution synthesis of monodispersed single-crystalline ZnO nanorods and derived hierarchical nanostructures

In this work, we report a room temperature wet-chemical approach to synthesize highly regulated, monodispersed ZnO nanorods and derived hierarchical nanostructures. In particular, ZnO has been prepared into single-crystalline conical or prismatic nanorods, and various hierarchical structures such as hexagonally branched, reversed umbrella-type, and cactus-like ZnO nanostructures comprising individual c-oriented nanorods. Depending on the synthetic conditions used, the diameter of nanorods can be controlled with a size down to 10-30 nm, while the aspect ratio can be controlled up to 50-100. Various preparative parameters, such as initial reactant concentrations, solvents, ligands, surfactants, precursor salts, and reaction time, have been systematically examined. Due to slow reactions at room temperature, excellent crystallinity and high morphological yield (100% in most cases) have been achieved via tuning the synthetic parameters. Our photoluminescence and UV measurements also confirm the attained crystal perfection and size uniformity.     

Shape-controllable synthesis of dendritic silver nanostructures at room temperature

In this communication, we demonstrated a simple chemical approach for preparing dendritic silver nanostructures by mixing AgNO₃ aqueous and o-phenylenediamine in the presence of NaCl solutions at room temperature. o-Phenylenediamine was found to act as a stabilizer as well as a reduction agent. Asformed silver dendrites were examined by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and Fourier transform infrared spectroscopy techniques. We found that the concentration of NaCl strongly influenced the shape of silver structures. The forming AgCl serve as efficient etchant and also produces single-crystal seeds. The possible formation mechanism is also discussed.     

Oriented attachment-based assembly of dendritic silver nanostructures at room temperature

How particles aggregate into an interesting dendritic structure has been the object of research for many years because of its importance in understanding physical processes involved and in designing novel materials. In this work, we for the first time describe an oriented attachment-based assembly mechanism for formation of different types of dendritic silver nanostructures at room temperature. It is found that the concentration of both AgNO(3) and p-aminoazobenzene (PA) molecules has a significant effect on the formation and growth of these novel nanostructures. Characterization by transmission electron microscopy (TEM) clearly shows that the dendritic silver nanostructures can be obtained through the preferential oriented growth along a crystallographically special direction. Interestingly, we observe that the oriented attachment at room temperature can also take place between relatively large single-crystalline silver particles with a diameter range from 20 to 60 nm, which may provide a new possibility for the design of novel metal nanostructures by using large metal nanoparticles as building blocks at room temperature. Moreover, a surface-enhanced Raman scattering (SERS) technique is used to investigate the role of PA molecules during the growth of the dendritic silver nanostructures.     

Polyaniline nanobelts, flower-like and rhizoid-like nanostructures by electrospinning

Nanobelts, flower-like and rhizoid-like nanostructures of pure polyaniline （PANI） doped with sulfuric acid or hydrochloric acid were prepared via electrospinning by using a coagulation bath as the collector after optimizing the fabrication parameters. The morphologies of these nanostructures were characterized by scanning electron microscope （SEM）. The possible formation mechanisms were discussed.     

Microcalorimetric Investigation on the lower critical solution temperature behavior of N-isopropycrylamide-co-acrylic acid copolymer in aqueous solution

The lower critical solution temperature (LCST) behaviors of random and segmented copolymers of N-isopropylacrylamide (NIPAM) and acrylic acid (AA) prepared in dioxane and water have been investigated by using ultrasensitive microcalorimetry (US-DSC). The introduction of AA increases the LCST of the former but slightly affects that of the latter. When the molar fraction of AA is low (approximately 2 mol %), the LCST of the segmented copolymer shifts to a higher temperature with increasing pH, while the LCST of the corresponding random copolymer slightly changes. Below the boiling point of water, the random copolymer and segmented copolymer with the molar fraction of AA about 15 mol % no longer exhibit an LCST at pH > 5. The addition of calcium ions leads the LCST of both the segmented copolymer and random copolymer to decrease. Our results suggest that the LCST behavior of the copolymers is determined by the clustering of poly(N-isopropylacrylamide) segments.     

Chromate nanorods/nanobelts: general synthesis, characterization, and properties

A general synthesis route to a family of single-crystal chromate nanorods/nanobelts has been established. The effects of pH and surfactant on phase and morphology of these microcrystalline materials have been investigated. The physical properties of the as-synthesized chromate nanocrystals such as dielectric, electrochemical, UV-vis absorbance, and photoluminescent properties have also been studied. The present general synthesis of various low-dimensional chromate nanomaterials provides useful information on the possible synthesis of other microcrystalline transition metal oxysalts.     

Controlled one-step fabrication of highly oriented ZnO nanoneedle/nanorods arrays at near room temperature

Highly oriented ZnO nanoneedle/nanorods arrays have been fabricated by direct oxidation of zinc foil in alkaline zincate ion solution at near room temperature (20 degrees C for nanoneedles, 30 degrees C for nanorods).     

Hydration and dynamic behavior of poly(N-isopropylacrylamide)s in aqueous solution: a sharp phase transition at the lower critical solution temperature

The number of hydrated water molecules per poly(N-isopropylacrylamide) monomer unit in homogeneous aqueous solution was determined to be 11 exactly and anew below the lower critical solution temperature of 32 degrees C employing high-frequency dielectric relaxation techniques.     

Seeded high yield synthesis of short Au nanorods in aqueous solution

Short gold nanorods of average lengths ranging between 20 and 100 nm (with corresponding aspect ratios of 2 and 4) were synthesized in excellent yield (approximately 97%). These nanorods were characterized by dark-field microscopy, UV-visible spectrophotometry, and transmission electron microscopy. Temporal evolution of rod shape had also been followed by UV-visible spectrophotometry and transmission electron microscopy and indicates that the nanorods briefly increase in length, then increase slightly in width, as they grow. The effect of the synthetic parameters on the rod dimension and yield was explored to find out suitable conditions to produce short nanorods; short nanorods have both plasmon bands in the visible region of the spectrum, which is a valuable property for sensor applications.     

Bio-friendly synthesis of ZnO nanoparticles in aqueous solution at near-neutral pH and low temperature

ZnO nanoparticles are synthesized using a new bio-friendly method. The experimental conditions are very mild: aqueous solution at near-neutral pH and 37 degrees C. The as-obtained nanoparticles show the stable wurtzite structure without the need of annealing. The two reagents used are aqueous solutions of zinc nitrate and buffer tris(hydroxymethyl)aminomethane. This is a standard nontoxic buffer and inert to a wide variety of chemicals and biomolecules, therefore extremely satisfactory for biochemical reactions. Furthermore, this is a polydentade ligand which adsorbs strongly on one or more surfaces of ZnO inhibiting its crystal growth and yielding nearly spherical ZnO nanoparticles. Our objective is to use the crystallization method described here for further incorporation of biomolecules as additives in the reaction solution, aiming at the formation of ZnO with new physical properties.     

A facile method for gold decoration of Te@CdTe nanorods in aqueous solution

Colloidal synthesis of metal-semiconductor hybrid nanostructures is mainly achieved in organic solution. In some applications of hybrid nanoparticles relevant in aqueous media, phase transfer of hydrophobic metal-semiconductor hybrid nanostructures is essential. In this work, we present a simple method for direct synthesis of water-soluble gold (Au) decorated Te@CdTe hybrid nanorods (NRs) at room temperature by using aqueous Te@CdTe NRs as templates, which were preformed by using CdTe nanocrystals (NCs) as precursor in the presence of hydrazine hydrate (N(2)H(4)). Our results showed that NRs were decorated with Au islands both on tips and along the surface of the NRs. The size and density of Au islands can be controlled by varying the amount of Au precursor (mixture of HAuCl(4) and thioglycolic acid (TGA)) and TGA/HAuCl(4) ratio. A possible growth mechanism for the Au decoration of Te@CdTe NRs is concluded as three steps: (1) the formation of AuTe(1.7) via the substitution reaction of Cd(2+) by Au(3+), (2) adsorption of Au-TGA complex onto the preformed AuTe(1.7) anchors and following reduction by CdTe and N(2)H(4), leading to the formation of small Au NCs, (3) Au NCs grow to bigger ones, followed by reduction of more Au precursor by N(2)H(4).     

Fabrication of size-controllable and luminescent dysprosium benzenetricarboxylate nanobelts at room temperature

Lanthanide-based coordination polymer Dy(1,3,5-BTC)(H₂O)₆ nanobelts were successfully synthesized on a large scale through an extremely simple approach at room temperature; the size of the nanobelts can be easily tuned from several to several hundred micrometers in length, 70–600 nm in width, and 10–100 nm in thickness by varying concentrations, solvent, and surfactant reasonably. In addition, the as-obtained dysprosium benzenetricarboxylate nanobelts exhibit the characteristic emission of the Dy³⁺ ions, making the belt-like coordination polymer have potential applications in building minioptoelectronic devices.     

Facile synthesis of PbTe nanoparticles and thin films in alkaline aqueous solution at room temperature

A novel, simple, and cost-effective route to PbTe nanoparticles and films is reported in this paper. The PbTe nanoparticles and films are fabricated by a chemical bath method, at room temperature and ambient pressure, using conventional chemicals as starting materials. The average grain size of the nanoparticles collected at the bottom of the bath is ∼25 nm. The film deposited on glass substrate is dense, smooth, and uniform with silver gray metallic luster. The film exhibits p-type conduction and has a moderate Seebeck coefficient value (∼147 μV K⁻¹) and low electrical conductivity (∼0.017 S cm⁻¹). The formation mechanism of the PbTe nanoparticles and films is proposed.     

Novel preparation of snowflake-like dendritic nanostructures of Ag or Au at room temperature via a wet-chemical route

In this letter we describe a novel but effective wet-chemical route for the simple preparation of snowflake-like dendritic nanostructures of Ag, which are homogeneous in size, carried out by directly mixing AgNO3 and p-phenylenediamine (PPD) aqueous solutions at room temperature. It reveals that such dendrites are aggregates of nanoparticles and highly crystalline in nature. It is found that the molar ratio of [PPD]/[Ag+] influences the final morphologies of the structures formed and that excessive PPD (the molar ratio of [PPD]/[Ag+] is higher than 1:1) is crucial to achieving dendrites. The possible dendritic growth mechanism is also predicted. This method can also be extended to the preparation of Au dendrites.     

Borylation of aryldiazonium salts at room temperature in an aqueous solution under catalyst-free conditions

A general and convenient borylation reaction of aryldiazonium tetrafluoroborate salts with B₂pin₂ has been developed. In this catalytic system, no catalyst, additional ligands or additives were required. The reaction proceeded smoothly in an aqueous solution, and a variety of arylboronates were isolated in moderate to excellent yields under mild reaction conditions.     

Construction of nanostructures in aqueous solution from amphiphilic glucose‐derived polycarbonates

Carbohydrates are the fundamental building blocks of many natural polymers, their wide bioavailability, high chemical functionality, and stereochemical diversity make them attractive starting materials for the development of new synthetic polymers. In this work, one such carbohydrate, d ‐glucopyranoside, was utilized to produce a hydrophobic five‐membered cyclic carbonate monomer to afford sugar‐based amphiphilic copolymers and block copolymers via organocatalyzed ring‐opening polymerizations with 4‐methylbenzyl alcohol and methoxy poly(ethylene glycol) as initiator and macroinitiator, respectively. To modulate the amphiphilicities of these polymers acidic benzylidene cleavage reactions were performed to deprotect the sugar repeat units and present hydrophilic hydroxyl side chain groups. Assembly of the polymers under aqueous conditions revealed interesting morphological differences, based on the polymer molar mass and repeat unit composition. The initial polymers, prior to the removal of the benzylidenes, underwent a morphological change from micelles to vesicles as the sugar block length was increased, causing a decrease in the hydrophilic–hydrophobic ratio. Deprotection of the sugar block increased the hydrophilicity and gave micellar morphologies. This tunable polymeric platform holds promise for the production of advanced materials for implementation in a diverse range of applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 432–440     

Synthesis and characterization of PbS nanorods in W/O microemulsion system

PbS nanorods have been successfully synthesized in water-in-oil (W/O) microemulsion containing non-ionic surfactant OP, n-pentanol, cyclohexane, and aqueous solution. The effects of the molar ratio of water to surfactant (ω₀), the concentration of reactants and the ageing time on the morphologies of PbS nanoparticles were investigated. The microstructures, morphologies and properties of the synthesized products were characterized by means of X-ray diffraction, transmission electron microscopy, and ultraviolet-visible (UV-VIS) absorption spectroscopy, respectively. The results showed that the synthesized rod-like products are composed of cubic phase PbS. These nanorods have an average diameter of about 100 nm, and an average length of about 500 nm. In the UV-VIS absorption spectrum, the absorption edge of PbS nanorods exhibit a blue shift compared with that of bulk PbS, indicating the quantum confinement effect of PbS nano-particles     

Methane in aqueous solution at 300 K

A Monte Carlo simulation for a methane molecule within a cluster of 202 water molecules is presented and compared with previous studies by Scheraga and Beveridge. Whereas the structural information obtained agrees with previous findings, the energy points to the need for a very large number of Monte Carlo steps and for a different algorithm to compute the partial molar internal energy.