Ultra-smooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle sizes of 200 nm or more. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances in small clusters. The high monodispersity of the particles we demonstrate should facilitate the self-assembly of nanoparticle clusters with uniform optical resonances, which could in turn be used to fabricate optical metafluids. Narrow size distributions are required not only to control the spectral features, but also the morphology and yield of clusters in certain assembly schemes. KEYWORDS:Gold nanospheres, plasmonics, monodisperse, chemical etching, Fano-like resonance. TOC Graphic 3Accepted version of ACS Nano 7 (12): 11064 (2013) In equilibrium, a nanoscale crystal adopts a polyhedral morphology to minimize its surface free energy. As a result, metallic nanoparticles grown near equilibrium form facets. [1][2][3] Although the plasmon resonances and ease of functionalization 4 make such particles promising 1 for bottom-up assembly of optical resonators 5,6 and isotropic metamaterials, 7 it is difficult to make structures whose optical properties are reproducible from one particle or one multiple-particle cluster to the next since the resonances are often sensitive to features such as sharp corners, 8 number of facets, 9 roughness, 10 and overall size and shape. 11 Moreover, the interparticle optical coupling varies significantly with nanometer-scale changes in gap distance 12 and orientation. 13 The ideal particle for self-assembly of plasmonic structures is therefore not a polyhedron, but a spherical crystal without facets or grain boundaries. However, producing such particles is a materials challenge, since spherical crystals are not stable under any growth conditions. Here we show that a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices, results in ultra-smooth, highly spherical monocrystalline gold particles. The etching process, which is functionally similar to (but chemically different from) that used to make monocrystalline silver nanospheres for surface-enhanced Raman spectroscopy, 14,15 effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances 16 in small assemblies. The cyclic process we demonstrate could be extended to other metals and, because it is scalable up to particle sizes of 200 nm or more, might be used to create strongly scattering particles for sensors, 17,18 electromagnetic resonators, 7 and oth...

Hierarchical hollow spheres of Fe2 O3 @polyaniline are fabricated by template-free synthesis of iron oxides followed by a post in- and exterior construction. A combination of large surface area with porous structure, fast ion/electron transport, and mechanical integrity renders this material attractive as a lithium-ion anode, showing superior rate capability and cycling performance.

The preparation of anisotropic colloidal particles by a simple yet versatile temperature-controlled swelling process is described. The resulting polymeric particles feature a surface dimple, the size and shape of which were determined by the amount of oil captured in particles and the interfacial tension between the three phases: polystyrene (PS), decane, and the suspending medium. Following the removal of free or physically adsorbed surfactant from the swollen particles, hydrophobic dimples were produced upon evaporation of the oil phase. We demonstrate the spontaneous assembly of these 'dimpled particles' into dumbbell shapes or trimers through a site-selective hydrophobic interaction.

Submicron emulsions could be produced via the tip-streaming process in a flow-focusing microfluidic device. In this article, the stability of the liquid cone and thread for tip-streaming mode could be significantly improved by employing a three-dimensional flow-focusing device, in which the hydraulic resistance was adjusted by modulating the channel heights in the flow focusing area, orifice, downstream and dispersed phase inlet channel. The pressure range for tip-streaming mode was enlarged significantly compared with two-dimensional flow-focusing devices. Therefore, monodisperse emulsions were produced under this tip-streaming mode for as long as 48 hours. Furthermore, we could control the size of emulsion drops by changing the pressure ratio in three-dimensional flow-focusing devices while the liquid cone was easily retracted during the adjustment of pressure ratio in two-dimensional flow-focusing devices. Furthermore, using the uniform submicron emulsion droplets as confining templates, polyethylene glycol (PEG) particles were produced with a narrow size distribution at the sub-micrometre scale. In addition, magnetic nanoparticles were added to the emulsion for magnetic PEG particles, which can respond to magnetic field and would be biocompatible.

The theoretical extinction coefficients of gold nanoparticles (AuNPs) have been mainly verified by the analytical solving of the Maxwell equation for an ideal sphere, which was firstly founded by Mie (generally referred to as Mie theory). However, in principle, it has not been directly feasible with experimental verification especially for relatively large AuNPs (i.e., >40 nm), as conventionally proposed synthetic methods have inevitably resulted in a polygonal shaped, non-ideal Au nanosphere. Here, mono-crystalline, ultra-smooth, and highly spherical AuNPs of 40-100 nm were prepared by the procedure reported in our recent work (ACS Nano, 2013, 7, 11064). The extinction coefficients of the ideally spherical AuNPs of 40-100 nm were empirically extracted using the Beer-Lambert law, and were then compared with the theoretical limits obtained by the analytical and numerical methods. The obtained extinction coefficients of the ideally spherical AuNPs herein agree much more closely with the theoretical limits, compared with those of the faceted or polygonal shaped AuNPs. In addition, in order to further elucidate the importance of being spherical, we systematically compared our ideally spherical AuNPs with the polygonal counterparts; effectively addressing the role of the surface morphology on the spectral responses in both theoretical and experimental manners.

β-FeOOH nanorod (NR) catalysts prepared by ultrasonic-irradiated chemical synthesis enabled lithium-air cells to have high round-trip efficiency and extremely low overpotential as well as an outstanding rate capability. Good catalytic activities of the β-FeOOH NR bundle could be ascribed to its crystal structure, which consists of 2 × 2 tunnels formed by edge- and corner-sharing Fe(O,OH)6 octahedra as well as to its one-dimensional morphology, which makes the configured electrode highly porous, indicating that the -OOH-based catalyst can be a good substitute for oxide-base catalysts in lithium-air batteries. The ultrasonic-irradiated chemical synthesis suggested here may be a good solution to optimize the morphology of catalyst materials for maximum catalytic activity.

The highly monodisperse PtRu (1:1) colloidal nanoalloy was prepared by the co-reduction of Pt(acac)2 and Ru(acac)3 precursors, deposited on a Vulcan carbon (Vc) support and subsequently treated by acetic acid to generate active PtRu/Vc catalyst, which showed a remarkable performance of catalytic activity in methanol oxidation.

Hollow nan': Hollow face‐centered cubic (fcc) Co nanoparallelepipeds were prepared by thermolysis of solid fcc CoO nanoparallelepipeds in oleylamine (see TEM image). The solid fcc CoO nanoparallelepipeds are reduced by the oleylamine surfactant to form hollow fcc Co nanoparallelepipeds. Voids and fcc Co are generated on the surface of the solid fcc CoO nanoparallelepipeds by the removal of oxide as carbon monoxide.