We report on grazing-incidence small-angle x-ray scattering (GISAXS) study of 3D nanoparticle arrays prepared by two different methods from colloidal solutions-layer-by-layer Langmuir-Schaefer deposition and spontaneous self-assembling during the solvent evaporation. GISAXS results are evaluated within the distorted wave Born approximation (DWBA) considering the multiple scattering effects and employing a simplified multilayer model to reduce the computing time. In the model, particular layers are represented by nanoparticle chains where the positions of individual nanoparticles are generated following a model of cumulative disorder. The nanoparticle size dispersion is considered as well. Three model cases are distinguished-no shift between the neighboring chains (AA stacking), a shift equal to half of the mean interparticle distance (AB stacking) and random shift between the chains. The first two cases correspond to vertically correlated nanoparticle positions across different chains. A comparison of the experimental GISAXS patterns with the model cases enabled us to distinguish important differences between the 3D arrays prepared by the two methods. In particular, laterally ordered layers without vertical correlation of the nanoparticle positions were found in the nanoparticle multilayers prepared by the Langmuir-Schaefer method. On the other hand, the solvent evaporation under particular conditions produced highly ordered 3D nanoparticle assemblies where both laterally and vertically correlated nanoparticle positions were found. 相似文献
We have previously described nanoparticle nanotubes (NPNTs), i.e., tubular metallic nanostructures comprising coalesced nanoparticles (NPs), obtained by passing citrate-stabilized metal (Au, Ag, Pd) NP solutions through aminosilane-modified nanoporous alumina membranes. Here we show that the mechanism of NPNT formation involves two stages: (i) electrostatic binding of a monolayer of metal NPs to the amine groups on the membrane pore walls; and (ii) accumulation of NP multilayers and room-temperature coalescence to form solid nanotubes. Free-standing NPNTs are obtained by post-dissolution of the membrane template. An improved fabrication apparatus enabled evaluation of the role of drying and other preparation parameters on the NP coalescence and NPNT formation and structure. Intermittent drying during the NP accumulation stage is necessary for the formation of solid NPNTs, while a slow flow rate of the colloid solution through the membrane pores and reversal of the flow direction promote the formation of more uniform and longer NPNTs. 相似文献
The degradation of Pt nanoparticles (NPs) in fuel cell cathodes leads to the loss of the precious metal catalyst. While the effect of NP size on Pt dissolution has been studied extensively, the influence of NP shape is largely unexplored. Because of the recent development of experimental methods to control the shape of metal NPs, rational guidelines/insights on the shape effects on NP stability are imperative. In this study, first-principles calculations based on density functional theory were conducted to determine the stability of 1–2 nm Pt NPs against Pt dissolution and coalescence with respect to NP shape. Toward dissolution, the stability of the Pt NPs increases in the following order: Hexagonal close-packed < icosahedral < cuboctahedral < truncated octahedral. This trend is attributed to the synergy of the oxygen adsorption strength and the local coordination of the Pt atoms. With respect to coalescence, the size of a NP is related to its propensity to coalesce or detach/migrate to form larger particles. The stability of the Pt NPs was found to increase in the following order: Hexagonal close-packed < truncated octahedral < cuboctahedral < icosahedral, and was correlated with the cohesive energies of the particles. By combining the characteristic stabilities of the shapes, new “metal-interfaced” Pt-based coreshell architectures were proposed that should be more stable than pure Pt nanoparticles with respect to both dissolution and coalescence.
A method for sintering nanoparticles by applying voltage is presented. This electrical sintering method is demonstrated using silver nanoparticle structures ink-jet-printed onto temperature-sensitive photopaper. The conductivity of the printed nanoparticle layer increases by more than five orders of magnitude during the sintering process, with the final conductivity reaching 3.7 × 10(7)?S?m(-1) at best. Due to a strong positive feedback induced by the voltage boundary condition, the process is very rapid-the major transition occurs within 2?μs. The best obtained conductivity is two orders of magnitude better than for the equivalent structures oven-sintered at the maximum tolerable temperature of the substrate. Additional key advantages of the method include the feasibility for patterning, systematic control of the final conductivity and in situ process monitoring. The method offers a generic tool for electrical functionalization of nanoparticle structures. 相似文献
Hydroxyapatite (HA, Ca10(PO4)6(OH)2) nanoparticles were synthesized using calcining calcium dihydrogenphosphate (Ca(H2PO4)2 · H2O), calcium hydroxide (Ca(OH)2), and polyethylene glycol (PEG) at 900 °C in an oxygen atmosphere. This one-step process yields HA nanoparticles with similar particle sizes (e.g., 50–80 nm) that are well-crystallized and non-aggregated. PEG is an important factor in controlling the particle size, crystal phase, and degree of aggregation in these HA particles. This conclusion is supported by results from a field-emission scanning electron microscope (FE-SEM), X-ray diffractometry (XRD), energy dispersive X-ray analysis (EDS), a high-resolution transmission electron microscope (HR-TEM), and dynamic light scattering (DLS). 相似文献
Owing to their structural dispersion, the catalytic properties of nanoparticles are challenging to characterize in ensemble-averaged
measurements. The single-molecule approach enables studying the catalysis of nanoparticles at the single-particle level with
real-time single-turnover resolution. This article reviews our single-molecule fl uorescence studies of single Au-nanoparticle
catalysis, focusing on the theoretical formulations for extracting quantitative reaction kinetics from the single-turnover
resolution catalysis trajectories. We discuss the single-molecule kinetic formulism of the Langmuir-Hinshelwood mechanism
for heterogeneous catalysis, as well as of the two-pathway model for product dissociation reactions. This formulism enables
the quantitative evaluation of the heterogeneous reactivity and the differential selectivity of individual nanoparticles that
are usually hidden in ensemble measurements. Extension of this formulism to single-molecule catalytic kinetics of oligomeric
enzymes is also discussed.
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