We have synthesized and investigated the anisotropic growth of interesting silver nanorice. Its growth is kinetically controlled at 100 °C, and both oriented attachment and Ostwald ripening are involved, with the former growth mode dominating the anisotropic growth of the nanorice along the ⟨111⟩ direction. This one-directional growth is initiated by an indispensable seed-selection process, in which oxygen plays a critical role in oxidatively etching twinned silver crystals. The inhibition of this process by removing oxygen essentially blocks the nanorice growth. Although increasing reaction temperature to 120 °C accelerates the one-dimensional growth along the ⟨111⟩ direction, further temperature increase to 160 °C makes the oriented attachment dominated one-directional growth disappear; instead, the diffusion-controlled two-dimensional growth leads to the emergence of highly faceted truncated triangular and hexagonal plates mainly bound by low energy faces of {111}. Interestingly, we also found that the longitudinal surface plasmon resonance of the nanorice structures is highly sensitive to the refractive index of surrounding dielectric media, which predicts their promising applications as chemical or biological sensors. Moreover, the multipolar plasmonic resonances in these individual nanorice structures are visualized in real space, using high-resolution electron energy-loss spectroscopy.Keywords: electron energy-loss spectroscopy; growth mechanism; multipolar plasmonic resonance; oriented attachment; silver nanorice; surface plasmon resonance;

SERS-active silver hierarchical assemblies are synthesized in solution by the assistance of small acid molecules. We here demonstrate the acid-directed self-assembly of metal nanoparticles (MNPs) into large systems with complex structures, without the application of any polymer surfactant or capping agent. It is verified that small acid molecules (citric acid, mandelic acid, etc.) incorporated into conventional solution chemistry can direct the assembly of MNPs into well-defined hierarchical structures. The constructed assembled structures with highly roughened surfaces can be highly sensitive SERS platforms, and the fabricated core–shell Ag wires show especially high SERS sensitivity toward the analyte melamine. The prepared Ag particles with hierarchical structures show no evident polarization-dependent SERS behavior, and this isotropic feature may be an advantage for highly sensitive SERS tags, since no certain incident polarization is required for molecule detection. We believe the subsequent addition of acid to induce formation of self-assembled structures can be a general synthetic platform to fabricate metal structures with complex morphologies.

High-yield uniform silver nanorices were synthesized by a facile polyol process without the introduction of shape-selected seeds. Nanorices exhibit two plasmon resonance peaks in the visible and near-infrared regions respectively due to their anisotropy. XRD patterns demonstrated the HCP phase coexists with the FCC phase in nanorices. The novel structure of nanorices was characterized by TEM study which shows that the intergrowth of FCC and a small amount of HCP phase, nanoscale FCC (111) twinning structure, and multimodulated structures formed by a complicated stacking sequence along the long axis direction. The correlation between morphology and microstructure is discussed.

We describe a surfactant-promoted reductive route for the shape-controlled synthesis of gold nanostructures by hydrothermal treatment of chloroauric acid in the presence of the surfactant hexadecyltrimethylammonium bromide (CTAB) without using reducing agent. The results show that the cationic surfactant CTAB provides the dual function of promoting AuIII reduction to Au0 and size- and shape-controlled synthesis of the gold nanocrystals. More importantly, the benefit of the present work stems from the first report on the controlled synthesis of gold nanostructures by hydrothermal treatment of chloroauric acid in the presence of the surfactant CTAB without using reducing agent. The kinetics of the reduction could be manipulated through changes in the CTAB concentration to produce gold nanostructures with shapes ranging from three-dimensional (3D) octahedra, triangles, to two-dimensional (2D) hexagonal nanoplates in high yields. Growth of gold nanostructures in the CTAB solution with concentration was monitored by microscopic and spectroscopic techniques.

We show that the spatial distribution of the electromagnetic (EM) field enhancement can be probed directly via dynamic evolution of surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) molecules as they diffuse into Ag@SiO2 core−shell nanoparticles. The porous silica shell limits the diffusion of R6G molecules toward inner Ag cores, thereby allowing direct observation and quantification of the spatial distribution of SERS enhancement as molecules migrate from the low to high EM fields inside the dielectric silica shell. Our experimental evidence is validated by the generalized Mie theory, and the approach can potentially offer a novel platform for further investigating the site and spatial distribution of the EM fields and the EM versus chemical enhancement of SERS due to molecular confinement within the Ag@SiO2 nanoshell.Keywords: electromagnetic field enhancement; nanoparticles; Raman scattering; silica; silver; spatial distribution

The interaction of light with metal nanoparticles leads to novel phenomena mediated by surface plasmon excitations. In this article we use single molecules to characterize the interaction of surface plasmons with light, and show that such interaction can strongly modulate the polarization of the emitted light. The simplest nanostructures that enable such polarization modulation are asymmetric silver nanocrystal trimers, where individual Raman scattering molecules are located in the gap between two of the nanoparticles. The third particle breaks the dipolar symmetry of the two-particle junction, generating a wavelength-dependent polarization pattern. Indeed, the scattered light becomes elliptically polarized and its intensity pattern is rotated in the presence of the third particle. We use a combination of spectroscopic observations on single molecules, scanning electron microscope imaging, and generalized Mie theory calculations to provide a full picture of the effect of particles on the polarization of the emitted light. Furthermore, our theoretical analysis allows us to show that the observed phenomenon is very sensitive to the size of the trimer particles and their relative position, suggesting future means for precise control of light polarization on the nanoscale.

We present a new algorithm to calculate the near-field distribution of scattered light of multiple nanospheres based on recursive order-of-scattering (OS) and the matrix inversion approaches, which avoids the divergent problem encountered in origin OS method at the resonance condition. Using this method, we investigate the light-transport properties of linear chains of Ag nanospheres. We found a maximum 3 dB damping length of 1.4 μm of the light propagation when the first sphere of the linear Ag spheres with the radius R=25 nm was illuminated. The optimal configurations that favor the photon energy transport are investigated as well.

SERS-active silver hierarchical assemblies are synthesized in solution by the assistance of small acid molecules. We here demonstrate the acid-directed self-assembly of metal nanoparticles (MNPs) into large systems with complex structures, without the application of any polymer surfactant or capping agent. It is verified that small acid molecules (citric acid, mandelic acid, etc.) incorporated into conventional solution chemistry can direct the assembly of MNPs into well-defined hierarchical structures. The constructed assembled structures with highly roughened surfaces can be highly sensitive SERS platforms, and the fabricated core–shell Ag wires show especially high SERS sensitivity toward the analyte melamine. The prepared Ag particles with hierarchical structures show no evident polarization-dependent SERS behavior, and this isotropic feature may be an advantage for highly sensitive SERS tags, since no certain incident polarization is required for molecule detection. We believe the subsequent addition of acid to induce formation of self-assembled structures can be a general synthetic platform to fabricate metal structures with complex morphologies.