Metal dimer nanojunction-magnetic material composites for magnetic field sensing.

Noble metal nanocrystals are used as high sensitivity optoelectronic sensors, such as surface-enhanced Raman scattering, SERS. The sensing performance of metal nanocrystals can be further improved by forming dimer nanojunctions with strong "plasmonic coupling". Since the strength of "plasmonic coupling" is highly sensitive to the sub-nanoscale spacing between plasmonic nanocrystals in nanojunctions, nanojunctions can be used to detect external stimuli that can change the spacing of nanocrystals in the nanojunction and thus change the sensitivity of the Raman scattering spectrum.

Effect of morphologies and compositions of silver-based multicomponent heterogeneous nanocrystals on the reduction of 4-nitrophenol.

Silver-based nanocrystals have excellent catalytic performance in various reactions, such as the reduction of 4-nitrophenol. The catalytic performance of nanocrystals varies with several parameters, including nanocrystal morphology, composition, and plasmon-induced hot electrons around nanocrystals. Here, highly heterogeneous nanocrystals (Au-Ag and AgS-Ag nanocrystals) fabricated on polymer films a seed-mediated method are used as catalysts for the reduction of 4-nitrophenol, and the effect of the morphology and composition of nanocrystals on the catalytic performance is investigated.

Investigation of the Performance of Heterogeneous MOF-Silver Nanocube Nanocomposites as CO Reduction Photocatalysts by In Situ Raman Spectroscopy.

Here, we fabricated two different heterogeneous nanocomposites, core-shell MOF-AgNC and corner MOF-AgNC, as photocatalysts for CO conversion by generating metal-organic frameworks (MOFs) on silver nanocube templates. These MOF-AgNC nanocomposites showed good CO adsorption features and high CO reduction reactivity. The performances of these MOF-AgNC nanocomposites in CO adsorption and CO reduction reactions can be characterized by in situ Raman spectrum measurement.

Combination of Plasmon-Mediated Photochemistry and Seed-Mediated Methods for Synthesis of Bicomponent Nanocrystals.

Plasmon resonances of metal nanocrystals resulted from free electrons oscillating around nanocrystals, leading to a strong electromagnetic field around them. Because these oscillating electrons possess higher energy than the original ones, also known as hot electrons, these were widely used as photocatalysts for various reactions. Also, the strength and distribution of the electromagnetic field around the nanocrystals strongly depended on their morphology and excited irradiation, which led to the reaction environment around nanocrystals being controllable.

Highly-efficient electrically-driven localized surface plasmon source enabled by resonant inelastic electron tunneling.

On-chip plasmonic circuitry offers a promising route to meet the ever-increasing requirement for device density and data bandwidth in information processing. As the key building block, electrically-driven nanoscale plasmonic sources such as nanoLEDs, nanolasers, and nanojunctions have attracted intense interest in recent years. Among them, surface plasmon (SP) sources based on inelastic electron tunneling (IET) have been demonstrated as an appealing candidate owing to the ultrafast quantum-mechanical tunneling response and great tunability.

Tunable Optical Property of Plasmonic-Polymer Nanocomposites Composed of Multilayer Nanocrystal Arrays Stacked in a Homogeneous Polymer Matrix.

Layer-by-layer (LbL) synthetic technique has been used to deposit multilayers composed of a wide range of materials including polymers, colloidal particles, and biomolecules. A more complex organization of nanocomponents-within layers (intralayer) and across layers (interlayer)-beyond simple deposition is required for manufacturing next-generation materials and devices. Recently, LbL was used to fabricate multilayer stacked polymer-nanocrystal nanocomposites composed of a stacking sequence of two immiscible polymer thin films.

Copper Sulfide Nanodisks and Nanoprisms for Photoacoustic Ovarian Tumor Imaging.

Transvaginal ultrasound is widely used for ovarian cancer screening but has a high false positive rate. Photoacoustic imaging provides additional optical contrast to supplement ultrasound and might be able to improve the accuracy of screening. Here, we report two copper sulfide (CuS) nanoparticles types (nanodisks and triangular nanoprisms) as the photoacoustic contrast agents for imaging ovarian cancer.

Imaging of Nanoscale Light Confinement in Plasmonic Nanoantennas by Brownian Optical Microscopy.

The strongly enhanced and confined subwavelength optical fields near plasmonic nanoantennas have been extensively studied not only for the fundamental understanding of light-matter interactions at the nanoscale but also for their emerging practical application in enhanced second harmonic generation, improved inelastic electron tunneling, harvesting solar energy, and photocatalysis. However, owing to the deep subwavelength nature of plasmonic field confinement, conventional optical imaging techniques are incapable of characterizing the optical performance of these plasmonic nanoantennas. Here, we demonstrate super-resolution imaging of ∼20 nm optical field confinement by monitoring randomly moving dye molecules near plasmonic nanoantennas.

Large optical nonlinearity enabled by coupled metallic quantum wells.

New materials that exhibit strong second-order optical nonlinearities at a desired operational frequency are of paramount importance for nonlinear optics. Giant second-order susceptibility has been obtained in semiconductor quantum wells (QWs). Unfortunately, the limited confining potential in semiconductor QWs causes formidable challenges in scaling such a scheme to the visible/near-infrared (NIR) frequencies for more vital nonlinear-optic applications.

Colloidal Plasmonic Nanocomposites: From Fabrication to Optical Function.

Plasmonic nanostructures are extensively used building blocks for engineering optical materials and device architectures. Plasmonic nanocomposites (pNCs) are an emerging class of materials that integrate these nanostructures into hierarchical and often multifunctional systems. These pNCs can be highly customizable by modifying both the plasmonic and matrix components, as well as by controlling the nano- to macroscale morphology of the composite as a whole.

Tunable and directional plasmonic coupling within semiconductor nanodisk assemblies.

Semiconductor nanocrystals are key materials for achieving localized surface plasmon resonance (LSPR) excitation in the extended spectral ranges beyond visible light, which are critical wavelengths for chemical sensing, infrared detection, and telecommunications. Unlike metal nanoparticles which are already widely exploited in plasmonics, little is known about the near-field behavior of semiconductor nanocrystals. Near-field interactions are expected to vary greatly with nanocrystal carrier density and mobility, in addition to properties such as nanocrystal size, shape, and composition.

Supramolecular precursors for the synthesis of anisotropic Cu₂S nanocrystals.

Copper alkanethiolates are organometallic precursors that have been used to form Cu2S nanodisks upon thermal decomposition. Here, we demonstrate that molecular assembly of Cu alkanethiolates into an ordered liquid crystalline mesophase plays an essential role in templating the disk morphology of the solid-state product. To examine this templating effect, we synthesize Cu alkanethiolate precursors with alkane tails of varying chain length and sterics.

Localized surface plasmon resonances of anisotropic semiconductor nanocrystals.

We demonstrate that anisotropic semiconductor nanocrystals display localized surface plasmon resonances that are dependent on the nanocrystal shape and cover a broad spectral region in the near-IR wavelengths. In-plane and out-of-plane dipolar resonances were observed for colloidal dispersions of Cu(2-x)S nanodisks, and the wavelengths of these resonances are in good agreement with calculations carried out in the electrostatic limit. The wavelength, line shape, and relative intensities of these plasmon bands can be tuned during the synthetic process by controlling the geometric aspect ratio of the disk or using a postsynthetic thermal-processing step to increase the free carrier densities.

Polyelectrolyte-templated synthesis of bimetallic nanoparticles.

Bimetallic nanoparticles (NPs) are known to exhibit enhanced optical and catalytic properties that can be optimized by tailoring NP composition, size, and morphology. Galvanic deposition of a second metal onto a primary metal NP template is a versatile method for fabricating bimetallic NPs using a scalable, solution-based synthesis. We demonstrate that the galvanic displacement reaction pathway can be controlled through appropriate surface modification of the NP template.