Self-Assembly of Gold Nanoparticles on Nanometre-Patterned Surface

The self-assembly processes of gold nanoparticles on nanometre-step-patterned Si surface and polished Si surface are investigated by the convective self-assembly method. The convective self-assembly method is used to deposit the colloids dispersed in benzene onto the substrates. The SEM results show that the configurations of the gold arrays depend on the surface morphology of the substrates. On the nanometre-step-patterned Si surface, the nanoparticles self assemble into parallel lines, and the distance between the neighbouring lines is around 35 nm. On the polished Si surface the nanoparticles form compact domains. In each domain the particles are closepacked in a two-dimensional hexagonal superlattice and are separated by uniform distances. The analysis shows that on the nanometre-step-patterned Si surface, the steps play critical roles in the self-assembly process of gold nanoparticles. The capillary force from the steps drives the particles to lines along the steps. Therefore, the particles tend to self-assemble into one-dimensional line structures when the solvent evaporates. For the polished Si substrate there is a little difference that the particles form two-dimensional hexagonal superlattices without the directional confinement.     

Uniform magnetic properties for an ultrahigh-density lattice of noninteracting co nanostructures

We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of 26 Tera/in2 (1 Tera=10(12)), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.     

Spatial characterization of the laser-induced plasma plumes generated by IR CO2 pulsed laser on carbon targets

We have used ferrocene and paraffin wax as novel precursor and solvent for the growth of iron oxide nanoparticles. The proposed method of growth has several advantages over existing methods of growth using iron pentacarbonyl a precursor. Highly crystalline and monodispersed particles are obtained which assemble in two- and three-dimensional hexagonal closed packed superlattices. Growth kinetics has been studied by varying concentration of the precursor and time of growth. A phenomenological model has been proposed to explain the growth kinetics.     

Laser-assisted growth of gold nanoparticles: Shaping and optical characterization

We demonstrate that supported gold nanoparticles with a given well-defined shape can be produced by laser-assisted growth. For this purpose, gold nanoparticles with average radii ranging from 1.5 to 13 nm, i.e., coverage between 0.45 × 10¹⁶ and 5.6 × 10¹⁶ atoms/cm², were prepared at room temperature by self-assembly of atoms deposited on quartz and sapphire substrates. For analysis of the samples, the optical spectra of the particles were measured with p-polarized light and photon energies in the range of 1.3 to 3.1 eV. Irradiating the particles during growth with laser light of different wavelengths to stimulate surface plasmon excitation made it possible to stabilize mean axial ratios between 0.19 and 0.98. The influence of the laser fluence on the shape of the nanoparticles was also investigated and shows that the position of the surface plasmon resonance shifts to higher energies as the fluence rises. Optimum growth conditions to shape gold nanoparticles with axial ratios close to unity (spheres) with a relatively low laser fluence of 60 ± 5 mJ/cm² have also been found. The results of our experiments show that laser-assisted growth is a powerfultechnique to control the shape of nanoparticles.     

Growth of gold nanoparticles on faceted O/Ru(11–20) nanotemplate

The growth of gold nanoparticles on the oxygen-covered faceted Ru(11–20) surface is investigated by scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES). By depositing gold onto the faceted surface held at room temperature, gold nanoparticles with regular spacings are fabricated. Gold nanoparticles are found to nucleate preferentially within valleys of the faceted surface. Our work demonstrates that the faceted metal surfaces are promising templates for the growth of metal nanoparticles.     

Gold Nanoparticles Obtained by Bio-precipitation from Gold(III) Solutions

The use of metal nanoparticles has shown to be very important in recent industrial applications. Currently gold nanoparticles are being produced by physical methods such as evaporation. Biological processes may be an alternative to physical methods for the production of gold nanoparticles. Alfalfa biomass has shown to be effective at passively binding and reducing gold from solutions containing gold(III) ions and resulting in the formation of gold(0) nanoparticles. High resolution microscopy has shown that five different types of gold particles are present after reaction with gold(III) ions with alfalfa biomass. These particles include: fcc tetrahedral, hexagonal platelet, icosahedral multiple twinned, decahedral multiple twinned, and irregular shaped particles. Further analysis on the frequency of distribution has shown that icosahedral and irregular particles are more frequently formed. In addition, the larger particles observed may be formed through the coalescence of smaller particles. Through modification of the chemical parameters, more uniform particle size distribution may be obtained by the alfalfa bio-reduction of gold(III) from solution.     

Low temperature and low pressure CO oxidation on gold clusters supported on MgO(100)

CO oxidation has been investigated on Au/MgO(100) model catalysts at RT and low pressure. The gold particles prepared by UHV evaporation on clean MgO surfaces are characterized by HRTEM. The gold particles are FCC single crystals or multiple twins with five-fold symmetry. Infrared spectroscopy indicates that two types of adsorption sites are present which correspond to loosely and strongly bound CO. The equilibrium CO coverage for the strongly bound CO is smaller than 0.1 ML. CO titration experiments show that oxygen does not dissociate on the gold nanoparticles. The CO oxidation reaction is studied at RT by molecular beam methods. A steady state CO reaction probability up to 0.50 is measured, for the first time at low pressure, for gold particles with a mean size of 1.5 nm. A reaction mechanism is proposed in which CO adsorbed on low coordinated gold atoms reacts with oxygen adsorbed molecularly, possibly at the Au/MgO interface.     

Bimetallic Nanoparticles with Exotic Facet Structures via Iodide‐Assisted Reduction of Palladium

Iodide is arguably the most challenging halide to control as a shape‐directing additive in metal nanoparticle synthesis and the addition of iodide during bimetallic nanoparticle growth often leads to inhomogeneously stellated products. Through judicious control of low micromolar concentrations of iodide ions in solution in a seed‐mediated approach, alloyed gold–palladium tetradecapod nanoparticles have been synthesized with a mixture of both well‐defined convex and concave surfaces. Notably, these particles are uniform and symmetrical, and this unusual combination of convex and concave features in a single nanostructure is not simply an artifact of intersecting spikes, as would be the case with stellated particles. Further, an important new role for iodide in catalyzing the reduction of palladium ions is identified, particularly at the edge sites of the growing gold nanoparticles. This differs from the commonly accepted theory that iodide slows metal ion reduction, and thus opens up promising new routes to the synthesis of other bimetallic nanoparticles with exotic shapes and surface structures.     

Synthesis and characterization of silica-gold core-shell (SiO<Subscript>2</Subscript>@Au) nanoparticles

This paper reports a systematic investigation of the growth and attachment of small gold nanoparticles to the functionalized surface of larger silica nanoparticles by three different methods. Nearly monodispersed silica particles and gold nanoparticles were prepared by sol-gel method. The size of the particle could be altered by changing the concentration of reactants, temperature and the time for which they react. The nanocoreshell particles prepared by three different methods were studied using scanning electron microscopy (SEM), UV-vis spectroscopy and Fourier transform infrared spectroscopy. We have found that the third method (c), a combination of the first two methods (a) and (b), has given better results.      

Flow Synthesis of Plasmonic Gold Nanoshells via a Microreactor

Gold nanoshells with tunable surface plasmon resonances are a promising material for optical and biomedical applications. They are produced through seed‐mediated growth, in which gold nanoparticles (AuNPs) are seeded on the core particle surface followed by growth of the gold seeds into a shell. However, synthetic gold nanoshell production is typically a multistep, time‐consuming batch‐type process, and a simple and scalable process remains a challenge. In the present study, a continuous flow process for the seed‐mediated growth of silica–gold nanoshells is established by exploiting the excellent mixing performance of a microreactor. In the AuNP‐seeding step, the reduction of gold ions in the presence of core particles in the microreactor enables the one‐step flow synthesis of gold‐decorated silica particles through heterogeneous nucleation. Flow shell growth is also realized using the microreactor by selecting an appropriate reducing agent. Because self‐nucleation in the bulk solution phase is suppressed in the microreactor system, no washing is needed after each step, thus enabling the connection of the microreactors for the seeding and shell growth steps into a sequential flow process to synthesize gold nanoshells. The established system is simple and robust, thus making it a promising technology for producing gold nanoshells in an industrial setting.     

Dynamical self-assembly of nanocrystal superlattices during colloidal droplet evaporation by in situ small angle x-ray scattering

The nucleation and growth kinetics of highly ordered gold nanocrystal superlattices during the evaporation of nanocrystal colloidal droplets was elucidated by in situ time-resolved small-angle x-ray scattering. We demonstrated for the first time that the evaporation rate can affect the dimensionality of the superlattices. The formation of two-dimensional nanocrystal superlattices at the liquid-air interface of the droplet has exponential growth kinetics that originates from interface crushing.     

Transport in superlattices of magnetic nanoparticles: coulomb blockade, hysteresis, and switching induced by a magnetic field

We report on magnetotransport measurements on millimetric superlattices of Co-Fe nanoparticles surrounded by an organic layer. At low temperature, the transition between the Coulomb blockade and the conductive regime becomes abrupt and hysteretic. The transition between both regimes can be induced by a magnetic field, leading to a novel mechanism of magnetoresistance. Between 1.8 and 10 K, a high-field magnetoresistance attributed to magnetic disorder at the surface of the particles is also observed. Below 1.8 K, this magnetoresistance abruptly collapses and a low-field magnetoresistance is observed.     

稀土纳米金对银染效果的影响及其UV-Vis吸收光谱

制备了La,Ce,Nd,Sm,Eu,Gd,Dy微粒和纳米金,分别用La,Ce,Nd,Sm,Eu,Gd,Dy微粒替代部分的纳米金,研究了La-Au,Ce-Au,Nd-Au,Sm-Au,Eu-Au,Gd-Au,Dy-Au微粒分别对银染效果的影响及其紫外可见(UV-Vis)吸收光谱。与纳米金相比,La-Au,Ce-Au,Nd-Au,Sm-Au,Eu-Au,Gd-Au,Dy-Au微粒可延长银染后的斑点持续的时间,其中Nd-Au微粒的效果最好,斑点持续的时间为30 min,是纳米金的2.7倍;可大幅度加深斑点的颜色,其中Nd-Au,Sm-Au微粒的效果最好,用Nd微粒替代部分的纳米金,纳米金用量降低了80%,但还能提高银染法的灵敏度。在200～800 nm范围,La,Ce,Nd,Sm,Eu,Gd,Dy微粒和纳米金溶液的UV-Vis吸收光谱只有一个吸收峰,λ_max分别为275,277,276,276,278,277,278和521 nm;La-Au,Ce-Au,Nd-Au,Sm-Au,Eu-Au,Gd-Au,Dy-Au微粒混合液的UV-Vis吸收光谱有两个吸收峰,λ_max(RE)和λ_max(Au)分别为276和522 nm,276和522 nm,276和523 nm,276和523 nm,276和522 nm,276和522 nm,276和523 nm,纳米金和La微粒的吸收峰的波长发生了红移,Ce,Eu,Gd,Dy微粒的吸收峰的波长发生了蓝移,Nd,Sm微粒的吸收峰的波长不变,纳米金与稀土微粒可能有相互作用。     

Low wavenumber Raman scattering of cobalt nanoparticles self‐organized in 3D superlattices far from surface plasmon resonance

We report the first observation of low wavenumber Raman scattering from cobalt nanoparticles under 514.5nm laser excitation. These 7.4nm diameter particles were self‐organized in 3D superlattices, but we assign the Raman signature to vibrations of the individual nanoparticles, according to Lamb's elastic sphere model. We estimate the relative Raman intensity to be around 500 times lower than it would be for silver nanoparticles, but our results demonstrate that surface plasmon–phonon resonance coupling is not mandatory to observe Lamb's modes in metal nanoparticles. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural and Optical Properties of Gold/Silica “Mushroom” Particles Prepared by Interfacial Templating

Complex shaped nanoparticles featuring structural or surface chemical patchiness are of special interest in both fundamental and applied research areas. This study reports the preparation and optical properties of gold/silica “mushroom” nanoparticles, where a gold particle is only partially covered by the silica cap. The synthetic approach allows precise control over the particle structure. The interfacial preparation method relies on partially embedding the gold particles in a polystyrene layer that masks the immersed part of the gold particle during silica shell growth from an aqueous solution. By adjusting sacrificial polystyrene film thickness and silica growth time, precise control over the coverage and cap thickness can be achieved. Correlative electron microscopy and single particle scattering spectroscopy measurements underline the high precision and reproducibility of the method. The good agreement between the measured and simulated single particle spectra supported by near‐field calculations indicates that the observed changes in the dipolar plasmon resonance are influenced by the extent of coverage of the gold core by the silica cap. The straightforward methods readily available for gold and silica surface modification using range of different (bio)molecules make these well‐defined nanoscale objects excellent candidates to study fundamental processes of programmed self‐assembly or application as theranostic agents.     

Gold nanoparticles: enhanced optical trapping and sensitivity coupled with significant heating

Gold nanoparticles appear to be superior handles in optical trapping assays. We demonstrate that relatively large gold particles (R(b)=50 nm) indeed yield a sixfold enhancement in trapping efficiency and detection sensitivity as compared to similar-sized polystyrene particles. However, optical absorption by gold at the most common trapping wavelength (1064 nm) induces dramatic heating (266 degrees C/W). We determined this heating by comparing trap stiffness from three different methods in conjunction with detailed modeling. Due to this heating, gold nanoparticles are not useful for temperature-sensitive optical-trapping experiments, but may serve as local molecular heaters. Also, such particles, with their increased detection sensitivity, make excellent probes for certain zero-force biophysical assays.     

Manganese–gold nanoparticles as an MRI positive contrast agent in mesenchymal stem cell labeling

We report a straightforward approach to prepare multifunctional manganese–gold nanoparticles by attaching Mn(II) ions onto the surface of 20 nm citrate-capped gold nanoparticles. In vitro MRI measurements made in agarose gel phantoms exhibited high relaxivity (18.26 ± 1.04 mmol⁻¹ s⁻¹). Controlled incubation of the nanoparticles with mesenchymal stem cells (MSCs) was used to study cellular uptake of these particles and this process appeared to be controlled by the size of the nanoparticle aggregates in the extracellular solution. SEM images of live MSCs showed an increased concentration of particles near the cell membrane and a distribution of the size of particles within the cells. Survivability for MSCs in contact with Mn–Au NPs was greater than 97% over the 3-day period and up to the 1 mM Mn used in this study. The high relaxivity and low cell mortality are suggestive of an enhanced positive contrast agent for in vitro or in vivo applications.     

Ripening of nanowire-supported gold nanoparticles

Gold nanoparticles have applications ranging from catalysts for low temperature oxidation of CO to solar energy capture in the infrared. For all these applications, particle size and shape are critical. In this study, nanoparticle gold formed on GaN nanowires by plasma-enhanced chemical vapor deposition was annealed at temperatures ranging from 150 to 270 °C for 24 h. Particle size was measured before and after annealing using a field emission scanning electron microscope. Ripening of the gold particles was observed even at the lowest annealing temperatures of the study. The particle growth kinetics showed an Arrhenius relationship with activation energy of 27.38 kJ/mol. This value suggests that ripening occurs by particle migration and coalescence rather than adatom diffusion.     

Effect of gold nanoparticle size on acoustic cavitation using chemical dosimetry method

When a liquid is irradiated with high intensities of ultrasound irradiation, acoustic cavitation occurs. Acoustic cavitation generates free radicals from the breakdown of water and other molecules. Cavitation can be fatal to cells and is utilized to destroy cancer tumors. The existence of particles in liquid provides nucleation sites for cavitation bubbles and leads to decrease the ultrasonic intensity threshold needed for cavitation onset. In the present investigation, the effect of gold nanoparticles with appropriate amount and size on the acoustic cavitation activity has been shown by determining hydroxyl radicals in terephthalic acid solutions containing 15, 20, 28 and 35 nm gold nanoparticles sizes by using 1 MHz low level ultrasound. The effect of sonication intensity in hydroxyl radical production was considered.The recorded fluorescence signal in terephthalic acid solutions containing gold nanoparticles was considerably higher than the terephthalic acid solutions without gold nanoparticles at different intensities of ultrasound irradiation. Also, the results showed that the recorded fluorescence signal intensity in terephthalic acid solution containing finer size of gold nanoparticles was lower than the terephthalic acid solutions containing larger size of gold nanoparticles. Acoustic cavitation in the presence of gold nanoparticles can be used as a way for improving therapeutic effects on the tumors.     

球型和棒状金纳米粒子的光谱性质比较

柠檬酸钠还原和诱导晶种生长法合成了球型和棒状金纳米粒子。金纳米粒子的吸收光谱表明,表面等离子体共振(SPR)强烈依赖于金属粒子的形状,球型粒子表现为单-SPR谱峰,而棒状粒子则具有横向和纵向SPR谱峰,且纵向SPR峰位和强度取决于棒状粒子的径横比。棒状金纳米粒子对吸附的对巯基苯甲酸分子的拉曼散射比球型金纳米粒子具有更强的表面增强性能,归因于棒状粒子高能晶面上的吸附可能导致的更强的化学增强效应。