Au@Pd core-shell nanobricks with concave structures and their catalysis of ethanol oxidation.

Au@Pd core-shell nanobricks (CNBs) with concave surfaces and Pd shells with a thickness of approximately 5 nm were synthesized by co-reduction of HAuCl4 and H2 PdCl4 in the presence of Au seeds and Ag ions. These as-synthesized concave CNBs exhibit significantly enhanced catalytic activity for the electrooxidation of ethanol in alkaline media compared to the commercially-used Pd black. The improved performance of the Au@Pd CNBs can be attributed to the exposed stepped surfaces, high-index facets, and the synergistic effects of the core and shell metals.

Synthesis of colloidal metal and metal alloy nanoparticles for electrochemical energy applications.

This Review is focused on the recent progresses in the synthetic approaches to the precise control of structure, size, shape, composition and multi-functionality of metal and metal alloy nanoparticles. Many of these strategies have been developed based on colloidal methods, and to limited extent, the galvanic and other methods. The shape, size and composition often govern the chemical and catalytic properties that are important for electrochemical energy applications. The structure-property relationship and the design in controllable structures and morphologies for specific reactions such as oxygen reduction reaction (ORR) are emphasized.

Gold mesoflower arrays with sub-10 nm intraparticle gaps for highly sensitive and repeatable surface enhanced Raman spectroscopy.

Self-assembling Au mesoflower arrays are prepared using a polymethylmethacrylate (PMMA) template on an iron substrate via a combined top-down/bottom-up nanofabrication strategy. The PMMA template with the holes around 300-500 nm in diameter is first fabricated by using polymer blend lithography on iron substrates, and the highly homogeneous Au mesoflower arrays with less than 10 nm intraparticle gaps are subsequently obtained by an in situ galvanic reaction between HAuCl4 solution and the iron substrate under optimal stirring of the solution as well as reaction time. Owing to the unique mesostructures and uniformity, Raman measurements show that the gold mesoflower arrays obtained demonstrated a strong and reproducible surface enhanced Raman scattering (SERS) enhancement on the order of ∼10(7)-10(8). The development of a SERS substrate based on the Au mesoflowers with high spatial density of hot spots, relatively low cost and facial synthesis provides a novel strategy for applications in chemical and biomolecular sensing.

Sodium chloride template synthesis of cubic tin dioxide hollow particles for lithium ion battery applications.

This paper describes a new synthesis and lithium ion charge-discharge property of tin dioxide (SnO(2)) hollow nanocubes. SnO(2) is one of the best-known anode materials for lithium-ion battery application because of its high lithiation-delithiation capacity. Hollow nanostructures with high surface area are preferred, because they accommodate large volume changes and maintain the structural stability of electrode materials during charge-discharge cycles. The SnO(2) hollow cubes made in this study had a discharge capacity of up to 1783 mA h g(-1) for the initial cycle and 546 mA h g(-1) after 30 cycles at a current density of 0.2 C between 0.02 and 2.0 V (vs Li/Li(+)).

Nanoparticle attachment on silver corrugated-wire nanoantenna for large increases of surface-enhanced Raman scattering.

Using three-dimensional finite-difference time-domain (FDTD) simulation, we described a systematic investigation on the electric field enhancement of the silver corrugated nanowires. The enhancement factor (EF) of surface-enhanced Raman scattering (SERS) for corrugated nanowires can be markedly increased by 1 or 2 orders of magnitude as compared with the smooth nanowires. Moreover, the EF can be further increased with nanoparticle attachment on the corrugated Ag nanowires owing to the coupling between the discrete plasmon state of the nanoparticles and continuum plasmon states of the corrugated nanowire or the crossed corrugated nanowires. The surface plasmonic field distribution of Ag nanowires can be effectively controlled by the polarization of the incident light. Raman spectrum measurements show that the relatively dense corrugated nanowires exhibit a relatively high reproducibility and SERS enhancement attributed to the elimination of polarization-dependent SERS-anisotropic enhancement via the overlapping of randomly distributed Ag nanowires. Such nanostructures as potential nanoantennas offer a route to optimize plasmon coupling for designing miniaturization integration.

Fabrication of ultrahigh-density nanowires by electrochemical nanolithography.

An approach has been developed to produce silver nanoparticles (AgNPs) rapidly on semiconductor wafers using electrochemical deposition. The closely packed AgNPs have a density of up to 1.4 × 1011 cm-2 with good size uniformity. AgNPs retain their shape and position on the substrate when used as nanomasks for producing ultrahigh-density vertical nanowire arrays with controllable size, making it a one-step nanolithography technique. We demonstrate this method on Si/SiGe multilayer superlattices using electrochemical nanopatterning and plasma etching to obtain high-density Si/SiGe multilayer superlattice nanowires.

Mesocrystals: syntheses in metals and applications.

Self-assembly of nanoparticles has emerged as a powerful technique to integrate nanoparticles into well-defined ensembles with collective properties that are different from those of individual nanoparticles and bulk materials with the same chemical composition. Compared with the classical ion/molecule-mediated crystal growth, particle-mediated crystallographically ordered self-assembly is considered as "non-classical crystallization" and the resultant product is termed a "mesocrystal". In this tutorial review, we begin by summarizing the progresses of this field during last decade. Secondly, we outline developments in related fields such as grain rotation and oriented attachment as well as mesocrystals. Thridly, the recent progress in the syntheses of mesocrystals particularly in metals, and the related properties are introduced. Finally, some of the current open questions are discussed.

Quantum confinement, surface roughness, and the conduction band structure of ultrathin silicon membranes.

We report direct measurements of changes in the conduction-band structure of ultrathin silicon nanomembranes with quantum confinement. Confinement lifts the 6-fold-degeneracy of the bulk-silicon conduction-band minimum (CBM), Delta, and two inequivalent sub-band ladders, Delta(2) and Delta(4), form. We show that even very small surface roughness smears the nominally steplike features in the density of states (DOS) due to these sub-bands. We obtain the energy splitting between Delta(2) and Delta(4) and their shift with respect to the bulk value directly from the 2p(3/2)-->Delta transition in X-ray absorption. The measured dependence of the sub-band splitting and the shift of their weighted average on degree of confinement is in excellent agreement with theory, for both Si(001) and Si(110).

Silver nanowires growth via branch fragmentation of electrochemically grown silver dendrites.

We have demonstrated a new protocol of synthesizing Ag nanowires via an electrochemical Ostwald ripening (OR) driven branch fragmentation mechanism; the branching rate of the Ag nanowires is significantly decreased by means of an electrodeposition under a strong applied-potential, following a relaxation process.

Growing hyperbranched polyglycerols on magnetic nanoparticles to resist nonspecific adsorption of proteins.

Hyperbranched polyglycerols were grown from magnetic nanoparticles (MNPs) via surface-initiated anionic ring-opening polymerization of glycidol. The modified MNPs were characterized by using TEM, XPS, TGA and FTIR. Hyperbranched polyglycerols resist the nonspecific adsorption of proteins on magnetic nanoparticles. The capability of hyperbranched polyglycerols is comparable favorably with the performance of methyloxy poly(ethylene glycol) (a linear mPEG with a molecular weight of 750) in resisting the adsorption of proteins.

1, 3-dipolar cycloaddition as a general route for functionalization of Fe(3)O(4) nanoparticles.

Triazole formation by 1, 3-dipolar cycloaddition reactions has been used to functionalize the surface of Fe(3)O(4) nanoparticles. Fe(3)O(4) particle samples with diameters around 22 nm were synthesized without any additional stabilizer, and were then treated with silane coupling agent to react with propargyl acid. The alkynyl group on the Fe(3)O(4) surface provides better conjugation efficiency with azide derivative molecules, which led to their attachment through the formation of a 1, 2, 3-triazole ring.

Effect of SiO2 coating layer morphology on TiH2 gas release characteristic.

In this study, a uniform and compact SiO2 film-coating layer was prepared on the surface of TiH2 particles by sol-gel method using inexpensive raw materials. The preparation process of SiO2-coated TiH2 particles and the effect of the coating layer morphology on the gas release characteristic were investigated in detail. When the pH value of TiH2 suspending solution is about 4.0 and the concentration of silicic acid is more than 0.5 mol/L, the coating layer shows a SiO2 particle-coating morphology. While a homogeneous and dense film-coating layer can be obtained when the solution pH value and concentration of silicic acid are about 4.0 and 0.5 mol/L. The results of gas release at 700 degrees C show that TiH2 particles coated with silicon dioxide layers can efficiently delay the starting time of gas release of TiH2 powders to 60-100 s. Comparing the particle-coating layer, the SiO2 film-coating layer has a better delaying effect on gas release of TiH2 particles.

The effect of SiO2 and Al2O3 coating on the surface of TiH2 powders on gas release.

TiH(2) particles coated with binary Al(2)O(3) and SiO(2) layers were prepared, and the effect of the coating layer on gas release characteristics was investigated. The results show that homogeneous and compact coating layers of SiO(2)/Al(2)O(3) on the surfaces of TiH(2) particles can efficiently delay the starting time of hydrogen release from TiH(2) powders to approximately 120 s.