Multiple Twinned Particles Research Articles

Synthesis of Finger-like Hyper-branched Gold Nanostructures and its Linear Optical Properties

In this work we have reported synthesis of finger-like hyper-branched Au nanostructures by seed mediated growth where multiple-twinned nanoparticles played an important role in the growth process. Cyclic multiple twinned particles showed a regular polyhedron structure due to the involvement of different growth processes and results in unique shape evolution on specific surface which depends on the specific formation modes and on the particular structure of the twin-related subunits. The formation of finger-like hyper-branched Au nanostructures has been confirmed by HRTEM images and also it has been found that the synthesized nanostructures exhibit interesting linear optical absorption and enhanced (by 175%) visible photoluminescence emission properties.

Synthesis of anisotropic nanostructures of silver for its possible applications in glucose and temperature sensing

Syntheses of anisotropic nanostructures of silver have been demonstrated by using a simple chemical synthesis route and the roles of temperature and reaction time in the anisotropic growth of the material have been reported. The role of multiple twinned particles in the anisotropic shape evolution and branching growth of synthesized silver nanostructures is demonstrated. The optical absorption and photoluminescence (PL) properties of the non-functionalized silver nanostructures have been studied in the UV–visible wavelength region and there exist two surface plasmon resonance (SPR) peaks, one called transverse surface plasmon resonance (TSPR) peak situated at smaller wavelength at ∼410–415 nm, and another called longitudinal surface plasmon resonance (LSPR) peak appearing at longer wavelength at ∼595–615 nm in the visible region. Intense PL emission spectra centered at ∼410 nm have been observed from the synthesized products obtained at lower temperature, whereas the PL spectra of higher temperature materials are divided into two broad peaks staying >100 nm apart at both sides of 410 nm. It has been demonstrated that the synthesized non-functionalized silver nanostructure can further be utilized for sensing of glucose and temperature. Tyndall effect experiment with the synthesized silver nanostructures dispersed in methanol has been performed and demonstrated the stability of the nanostructures.

On the twinning and special grain boundaries of bimetallic particles via pulsed laser ablation of bulk AuCu in a vacuum

Bimetallic particles were formed by pulsed laser ablation of bulk AuCu in a vacuum and characterized by X-ray diffraction and transmission electron microscopy. The fcc-type AuCu3 and Cu-doped Au nanocondensates ca. 5 nm in size were coalesced over {001} and ~{111} vicinal surfaces to form quasi multiple twinned particles with solute/vacancy entrapped [110]{hkl} tilt boundaries with a symmetric {111}/{111} interface as well as asymmetric {001}/{111} and {331}/{112} interfaces. Polysynthetic {111} twinning due to strain relaxation and the shock effect was also observed for the alloyed particulates and nanocondensates.

The Role of Etching in the Formation of Ag Nanoplates with Straight, Curved and Wavy Edges and Comparison of Their SERS Properties

We investigate the role of etching in the formation of Ag nanoplates with different morphologies. By examining the reduction of AgNO3 with poly(vinyl pyrrolidone) in an aqueous solution under a hydrothermal condition, we confirm that etching plays an essential role in promoting the growth of Ag triangular nanoplates with straight edges at the expense of multiple twinned particles via Ostwald ripening. Once all the multiple twinned particles are gone, etching will continue at the corners of nanoplates, leading to the formation of enneahedral nanoplates with curved edges. When the nanoplates with straight edges are transferred into ethanol and subjected to a solvothermal treatment, we obtain nanoplates with wavy edges and sharp corners due to etching on the edges. A comparison study indicates that, at the same particle concentration, Ag nanoplates with wavy edges embraces a SERS enhancement factor at least 6 and 13 times stronger than those with straight and curved edges, respectively. The results from finite difference time domain calculations support our experimental observation that the sharp features on nanoplates with wavy edges are the most active sites for SERS.

Citrate-Free Synthesis of Silver Nanoplates and the Mechanistic Study

We report a citrate-free synthesis of Ag nanoplates with an edge length of 50 nm that involved the reduction of AgNO3 by poly(vinyl pyrrolidone) (PVP) in ethanol at 80 °C under a solvothermal condition. Within a period of 4 h, greater than 99% of the initially added AgNO3 could be converted into Ag nanoplates with excellent stability. To understand this remarkably simple and efficient process, we systematically investigated the roles played by various reaction parameters, which include the type of precursor, reducing powers of PVP and ethanol, molar ratio of PVP to AgNO3, solvent, involvement of O2, and effects of pressure and temperature. Our results suggest a plausible mechanism that involves (i) fast reduction of AgNO3 to generate Ag multiple twinned particles (MTPs) via a thermodynamically controlled process, (ii) kinetically controlled formation of plate-like seeds and their further growth into small nanoplates in the presence of Ag(+) ions at a low concentration, and (iii) complete transfer of Ag atoms from the MPTs to nanoplates via O2-mediated Ostwald ripening. We demonstrated that the molar ratio of PVP to AgNO3 in ethanol plays an essential role in controlling the reduction rate for the formation of MTPs and plate-like seeds under the solvothermal condition, transformation kinetics, and final morphology taken by the Ag nanoplates. In particular, when the reaction temperatures were above the boiling point of ethanol, the pressure induced by a solvothermal process accelerated the oxidative etching of Ag MTPs to facilitate their complete conversion into nanoplates. The mechanistic insight could serve as a guideline to optimize the experimental parameters of a solvothermal synthesis to control the reduction kinetics and thus the formation of metallic nanocrystals with controlled shapes and in high yields and large quantities.

Temperature effects in carbon monoxide and methanol electrooxidation on platinum–ruthenium: influence of grain boundaries

The temperature dependence of methanol and CO monolayer oxidation is studied on carbon-supported PtRu (1:1 atomic ratio) electrodes with different metal percentages (5, 30, and 60 wt.%) in an aqueous H2SO4 electrolyte. High-resolution transmission microscopy confirms that at high (30 or 60 wt.%) metal percentage PtRu nanostructures with a high concentration of intercrystalline boundaries are formed. These nanostructures comprise multiple-twinned particles, particles with intersecting randomly oriented intergrain boundaries, or particles with parallel intergrain boundaries. Formation of such nanostructures leads to a decrease of the apparent activation energy of the methanol and CO monolayer oxidation, while the Tafel slope and the reaction order in methanol show minor dependence on the type of nanostructure. Materials with a high concentration of grain boundary regions may be of interest for practical applications in direct methanol or proton exchange fuel cells fed with reformate.

One-Pot Synthesis of Monodispersed Silver Nanodecahedra with Optimal SERS Activities Using Seedless Photo-Assisted Citrate Reduction Method

This article presents a mechanistic study of silver nanodecahedra prepared by the method of photoassisted sodium citrate reduction under irradiation of blue light-emitting diodes (LEDs). This synthesis of silver nanodecahedra can be easily reproduced in the absence of silver seeds and can be completed in one-pot. The data suggest a combination of two processes including gradual growth from multiple-twinned particles and subsequent plasmon-mediated crystal growth. More than 85% of as-prepared silver nanoparticles are decahedra with edge lengths of 43.5 ± 5.2 nm. In addition, the as-prepared silver colloids exhibit a spectroscopic enhancement in comparison with spherical silver nanoparticle colloids and silver nanoprism colloids in the measurement of surface enhanced Raman spectroscopy (SERS) spectra of Rhodamin 6G, and with the decahedral silver colloids synthesized in the presence of PVP for detecting SERS signal of Rhodamin 6G. Overall, this photoassisted citrate reduction process is simple, and highly r...

A modified polyol process for growing Ag nanowires and nanoplates using 2-ethoxy ethanol

A modified polyol process was proposed to prepare Ag nanowires in this study. The typical reductant, ethylene glycol, was replaced with 2-ethoxy ethanol in the presence of polyvinylpyrrolidone (PVP) to grow Ag nanowires and nanoplates. The growth of Ag nanowires was monitored by the UV–Visible spectrum, which depends on the geometry-dependent surface plasmon resonances of the Ag nanowires. The crystal phase of the Ag nanostructures was identified by X-ray diffraction. Transmission electron microscopy showed that the average dimensions of the Ag nanowires were lengths of approximately 2–10 μm and diameter of 80 nm. The PVP molecules played a key role in directing the growth of the Ag nanostructures along the (111) crystal plane, and the reduction rate of Ag+ at 25 °C when 2-ethoxy ethanol was used was faster than when ethylene glycol was used, which improved the growth of the Ag nanowires. When the AgNO3-to-PVP ratio was adjusted to 2, multiple twinned particles could be observed at an initial stage of the reaction, and a higher yield of the Ag nanowires was synthesized. When the PVP drop rate was slowed, more Ag nanowires were grown. Interestingly, when the AgNO3 and PVP molecules were initially premixed, Ag nanoplates were generated, rather than nanowires, at a higher temperature in this reduction system.

Redispersion of Gold Multiple-Twinned Particles during Liquid-Phase Hydrogenation

Controlling the particle size of supported metal catalysts is essential to achieving active, selective, and stable catalysts. High-resolution electron microscopy has revealed that large Au particles (∼8 nm), supported on titania and if multiple-twinned, broke up into small particles (2–3 nm) during liquid-phase hydrogenation. Multiple-twinned Au particles, obtained after gas-phase reduction of as-prepared Au/TiO2 at elevated temperature, break up into smaller particles. EXAFS confirmed that the multiple-twinned particles were agglomerates of smaller particles. In contrast, calcination caused a strong interaction between Au and titania and the formation of mainly single crystalline Au particles (4 to 5 nm), which were relatively stable during liquid-phase hydrogenation. Reduction and calcination lead to gold particles that are fundamentally different.

Solar energy assisted palladium nanoparticles synthesis in aqueous medium

A new approach for the synthesis of palladium nanoparticles using the concept of concentrated solar energy has been developed. The use of citric acid as a greener reducing agent and polyvinyl pyrrolidone (PVP) as a capping agent with palladium precursor assists the synthesis of multiple twinned particles in aqueous reaction medium. Solar energy was concentrated using Fresnel lens. The effect of irradiation time on crystal growth has been studied. This is the first report wherein concentrated solar energy concept was used for the palladium nanoparticle (PdNP) synthesis. Application of solar energy over conventional energy sources makes this protocol environmentally benign.

Nitrate Ion Promoted Formation of Ag Nanowires in Polyol Processes: A New Nanowire Growth Mechanism

In polyol processes, it was widely accepted that Ag nanowires (NWs) were formed via uniaxial growth of multiple twinned decahedral particles (MTPs) along the {111} facets. Herein, we show that the above MTP uniaxial growth mechanism for growth of nanorods (NRs) and short nanowires (NWs) is different from that for the growth of long Ag NWs. We provide experimental evidence to show that polycrystalline long Ag NWs (up to ~100 μm) could be formed in high yield (~90%) by a completely different growth mechanism via self-assembly of Ag NPs/NRs. Transmission electron microscope (TEM) measurements show that long Ag NWs are composed of crystalline Ag NPs and NRs with multiple crystal orientations, and many NRs have crystalline structures with pentagonal cross section. Solution phase in situ X-ray diffraction (XRD) measurements show that a strained face-centered tetragonal (fct) phase was gradually formed during the formation and growth of long Ag NWs, in addition to the normal face-centered cubic (fcc) phase. The strained fct phase disappears after partial etching by HAuCl(4) and Fe(NO(3))(3). The working conditions for the MTP uniaxial growth mechanism and the current nitrate-promoted self-assembly growth mechanism will be compared and discussed.

Structural investigations on nanocrystalline Ni–W alloy films by transmission electron microscopy

Electrodeposited Ni–W alloys have been investigated in the as-deposited state by transmission electron microscopy in order to investigate the microstructural features in dependence of the tungsten content. Within the tungsten content range from 7 at.% up to 12 at.%, the microstructure is nanocrystalline characterized by a bimodal grain size distribution, consisting out of 20 to 200 nm sized grains and also larger grains with several 100 nm characteristic dimension. No clear trend in microstructure formation is visible with W content or deposition conditions in the investigated W content range. Only solid solution phase characteristics were observed. The lattice constant is 0.360 nm for 12 at.% W as derived from electron diffraction for the solid solution face centered cubic structure. Larger grains show twinning and stacking faults. Voids with diameter of a few nm were detected along with some multiple twinned particles, indicating high stress level during growth. About 2 at.% difference in the alloy composition from grain to grain was measured.

Polymer Driven Covalently Bonded Decahedral-Twinning of Ag Nanoparticles Prepared by ICP Enhanced Magnetron Sputtering Method

In this paper, an inductively coupled plasma (ICP) enhanced magnetron sputtering (MS) method was utilized to deposit silver (Ag) nanoparticles embedded inside of simultaneously polymerized poly(ethylene oxide) (PEO) thin film. Ex situ transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) have been employed to elucidate the Ag nanoparticle structure, shape, and growth process during ICP enhanced MS deposition. The results showed that, when capped by polymer PEO film, the Ag nanocrystals were shaped in multiple-twinned particles (MTP) and further transformed into decahedrons held five-twinning structure with distinct twinning boundaries. The formation of particle size of Ag nanocrystalline on Si (100) surfaces was found unambiguously dependent on the ICP power, and the estimated particle size of Ag nanoparticles was in the range of 5―10 nm. From the results, it was assumed that PEO coating was the reason for inducing the formation of Ag MTP and nanodecahedron structures.

Sonochemical formation of nanocrystalline gold in aqueous solution

Gold nanoparticles were prepared by the sonochemical reduction of the aqueous solution of HAuCl4 containing only a little 1-propanol in the present of sodium dodecyl sulfate. The sonochemically synthesised Au nanoparticles were characterised by TEM and UV–vis spectroscopy. Transmission electron microscopy has shown that several different types of gold particles are present, such as tetrahedral plate, decahedral, hexagonal plate and icosahedral multiple twinned particles.

Size-dependent structural transition from multiple-twinned particles to epitaxial fcc nanocrystals and nanocrystal decay

The size dependence of structural transition from multiple-twinned particles (MTP) to epitaxial face centered cubic nanocrystals was investigated for Ag nanoparticles formed on Si(001) surfaces by in situ reflection high-energy electron diffraction and ex situ transmission electron microscopy. The transition from MTP to nanocrystals was promoted by postdeposition annealing. Clear particle size dependence is found in the epitaxial formation temperatures $({T}_{E})$, which is about $2∕3$ of the calculated, size-dependent, melting temperature $({T}_{M})$ using the value of surface energy ${\ensuremath{\gamma}}_{S}=1.2\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2}$ for larger particles $(>2\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$. Once nanocrystals are formed, they decay and disappear in a narrow temperature range between 795 and $850\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. No evidence of nanocrystal melting was detected from the reflection high-energy electron diffraction observations.

Thermodynamic-Controlled Gas Phase Process for the Synthesis of Nickel Nanoparticles of Adjustable Size and Morphology

Gas phase processes are a successful route for the synthesis of nano materials. Nickel particles are used in applications ranging from catalysis to nano electronics and energy storage. The application field defines the required particle size, morphology, crystallinity and purity. Nickel tetracarbonyl is the most promising precursor for the synthesis of high purity nickel particles. Due to the toxicity of this precursor and to obtain an optimal process control we developed a two-step flow type process. Nickel carbonyl and nickel particles are synthesized in a sequence of reactions. The particles are formed in a hot wall reactor at temperatures below 400°C in different gas compositions. Varying the process conditions enables the adjustment of the particle size in a range from 3 to 140 nm. The controllable crystalline habits are polycrystalline, single crystals or multiple twinned particles (MTP). Spectroscopic investigations show an excellent purity. We report about the process and first investigations of the properties of the synthesized nickel nanomaterial.

Shape and Internal Structure of Silver Nanoparticles Embedded in Glass

The structural characteristics of silver nanoparticles embedded in glass by various routes of fabrication were studied in detail using high-resolution electron microscopy to find out if they are influenced by interaction with the surrounding glass matrix. Besides the formation conditions, the strength of the interaction between metal and glass governs the size-dependent changes of lattice spacings in such nanoparticles. However, determination of these changes is not straightforward because of complicated particle configurations and the interference nature of the lattice imaging technique. Imaging of lattice plane fringes and careful diffractogram analysis allowed the exclusion of any kind of tetragonal lattice distortion or transformation to hexagonal lattice type that may be deduced at first sight. Instead, the formation of twin faults in these nanoparticles turned out to be the essential structural feature and the main source of confusion about the lattice structure observed. The variety of particle forms is comparable to particles supported on oxide carriers. It is composed of single-crystalline particles of nearly cuboctahedron shape, particles containing single twin faults, multiple twinned particles containing parallel twin lamellae, and multiple twinned particles composed of cyclic twinned segments arranged around axes of 5-fold symmetry. The more twin planes involved in the particle composition, the more complicated is the interpretation of lattice spacings and lattice fringe patterns due to superposition of several twin segments.

Nanoparticles in interlayers of Bi 2O 3-doped ZnO ceramics

Nanoparticles found in interlayers between the grains of Bi 2O 3-doped ZnO were analyzed using electron diffraction, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. Both ZnO multiple twinned particles (MTPs) and single nanoparticles of less than 5 nm in diameter were found in the Bi-poor interlayers. The MTPs with the wurtzite structure give rise to no defects or structural changes in the present size because the angular misgap of five-fold symmetry is very small. Furthermore, β-Bi 2O 3 nanoparticles reaching a few tens of nanometers in diameter were formed in the Bi-rich interlayers.

Identification of active sites and influence of real structure of gold catalysts in the selective hydrogenation of acrolein to allyl alcohol

We have successfully employed oxide supported gold catalysts in the gas-phase hydrogenation of acrolein, the α,β-unsaturated aldehyde being most difficult to hydrogenate at the carbonyl group. The relation of structural characteristics and surface state of these catalysts with respect to their activity and selectivity have been studied by surface analytical techniques and high-resolution transmission electron microscopy which was carried out to elucidate the real crystal structures of gold particles. The performance of gold catalysts formed by various preparation and pretreatment procedures was strongly dependent on the reduction time: Increasing the latter resulted in a high number of multiple twinned gold particles which decrease both the selectivity to the desired product, allyl alcohol, and the turnover frequency. Furthermore, it has been demonstrated for the first time that the addition of a second metal (indium) results in a selective decoration of the faces of nanosized gold particles leaving edges free. The active sites of supported gold catalysts, favoring the adsorption of C=O group of acrolein and subsequent reaction to allyl alcohol, have been identified as edges of gold nanoparticles. The zinc oxide supported bimetallic Au-In catalyst produced allyl alcohol with a selectivity of 63% which is comparable to the best hydrogenation catalysts for this reaction.

Twinned b.c.c. spherical particles in a partially crystallized Ti 50Ni 25Cu 25 melt-spun ribbon

Some micrometric spherical particles containing several b.c.c. grains are obtained from an initially amorphous Ti 50Ni 25Cu 25 melt-spun ribbon after a controlled thermal treatment. The microstructure and crystallography of these crystalline particles have been investigated by TEM, showing that each of the grains grows to the same distance from the center of the particle, keeping the isotropic growth of the entire system. The number of grains in each particle is variable, but self-accommodating arrangements have always been found. Most of the grains show {112} B2 (sometimes {114} B2) planes unchanged when moving to an adjacent grain, as typical twin crystals. However, the interfaces between adjacent grains usually do not match with these invariant planes. The morphology and self-accommodating arrangements found in these multi-grain particles are unusual for b.c.c. structures, but resemble in some way the case of multiple twinned particles present in other materials, as the five-fold twinned structures in f.c.c. systems.