Effective medium theory characterization of Au/Ag nanoalloy-porous alumina composites

Three Millennia of Nanocrystals

The broad deployment of nanotechnology and nanomaterials in modern society is increasing day by day to the point that some have seen in this process the transition from the Silicon Age to a new Nano Age. Nanocrystals─a distinct class of nanomaterials─are forecast to play a pivotal role in the next generation of devices such as liquid crystal displays, light-emitting diodes, lasers, and luminescent solar concentrators. However, it is not to be forgotten that this cutting-edge technology is rooted in empirical knowledge and craftsmanship developed over the millennia. This review aims to span the major applications in which nanocrystals were consistently employed by our forebears. Through an analysis of these examples, we show that the modern-age discoveries stem from multimillennial experience passed on from our proto-chemist ancestors to us.

Vertically Aligned AgxAu1-x Alloyed Nanopillars Embedded in ZnO as Nanoengineered Low-Loss Hybrid Plasmonic Metamaterials

Hybrid plasmonic metamaterials offer a pathway to exotic properties and technologically important applications including subdiffraction imaging and plasmonic energy harvesting. Challenges remain for practical applications including high absorption losses of noble metals and tedious growth/fabrication processes. In this work, a self-assembled hybrid plasmonic metamaterial consisting of anisotropic Ag_xAu_1-x alloy nanopillars embedded in a ZnO matrix has been successfully grown. The chemical composition of the nanoalloy was determined to be Ag₆₁Au₃₉. The microstructure and optical properties arising from ZnO-Ag₆₁Au₃₉ alloyed hybrid systems were investigated and compared with that of the ZnO-Ag particle-in-matrix nanocomposite and the ZnO-Au vertically aligned nanocomposite. The ZnO-Ag₆₁Au₃₉ hybrid system demonstrates anisotropic morphology, excellent epitaxial quality, and enhanced optical properties, including surface plasmon resonance, hyperbolic dispersion, low absorption losses, and numerous epsilon-near-zero permittivity points, making it a promising candidate for practical applications of hybrid plasmonic metamaterials.

Highly Efficient and High Peak Transmittance Colorful Semitransparent Organic Solar Cells with Hybrid-Electrode-Mirror Microcavity Structure

Microcavity is an efficient approach to manufacture colorful semitransparent organic solar cells (ST-OSCs) with high color purity by tailoring the transmission spectrum to narrow peaks. However, in this type of colorful semitransparent devices, high power conversion efficiency (PCE) and high peak transmittance are not yet simultaneously achieved. This paper proposes a new type of microcavity structure to achieve colorful ST-OSCs with both high PCE and high peak transmittance, in which a hybrid Au/Ag electrode is used as a mirror and WO₃ is used as a spacer layer. First, it is demonstrated that the hybrid Au/Ag electrode mirror brings about an improvement of 7.7 and 5.5% for PCE and peak transmittance, respectively, when compared with those of the reference devices using the Ag electrode mirror. Specifically, the PCE of the optimized devices reaches the satisfactory value of over 9%, and the peak transmittance is over 25%. This value of PCE is the highest one reported so far for the microcavity-based ST-OSCs with the same peak transmittance. Second, it is demonstrated that the second-order resonance of the microcavity can be used to improve the color purity of green ST-OSCs by narrowing the transmission peak, and the combination of the second-order and third-order resonance can be used to construct colorful ST-OSCs with mixed colors. Thus, a novel approach is developed to tune the color of ST-OSCs, which is based on high-order resonance modes of the microcavity.

Nanosilver rainbow: a rapid and facile method to tune different colours of nanosilver through the controlled synthesis of stable spherical silver nanoparticles

A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles of different sizes producing distinct optical properties in aqueous solution at ambient temperature has been developed.

Molecular recognition by gold, silver and copper nanoparticles

The intrinsic physical properties of the noble metal nanoparticles, which are highly sensitive to the nature of their local molecular environment, make such systems ideal for the detection of molecular recognition events. The current review describes the state of the art concerning molecular recognition of Noble metal nanoparticles. In the first part the preparation of such nanoparticles is discussed along with methods of capping and stabilization. A brief discussion of the three common methods of functionalization: Electrostatic adsorption; Chemisorption; Affinity-based coordination is given. In the second section a discussion of the optical and electrical properties of nanoparticles is given to aid the reader in understanding the use of such properties in molecular recognition. In the main section the various types of capping agents for molecular recognition; nucleic acid coatings, protein coatings and molecules from the family of supramolecular chemistry are described along with their numerous applications. Emphasis for the nucleic acids is on complementary oligonucleotide and aptamer recognition. For the proteins the recognition properties of antibodies form the core of the section. With respect to the supramolecular systems the cyclodextrins, calix[n]arenes, dendrimers, crown ethers and the cucurbitales are treated in depth. Finally a short section deals with the possible toxicity of the nanoparticles, a concern in public health.

Tuning color by pore depth of metal-coated porous alumina

A simple and effective color tuning method has been developed by controlling the pore depth of the metal-coated porous alumina (PA) template. The mechanism for color tuning in this method was uncovered, which can be used to design a colorful complex pattern. A colorful 'world map' was produced and exhibited on a PA template by this method. Such vivid color tuning is predominantly due to the interference enhancement of the nanostructure. This method has the potential for tuning colors and being widely applied in the fields of nanotechnology, physics and photonics.

Application of anisotropic silver nanoparticles: multifunctionalization of wool fabric

Anisotropic silver nanoparticles (NPs) were successfully employed to color the wool fabrics in this study. The modified wool fabrics exhibited brilliant colors due to the localized surface plasmon resonance (LSPR) properties of silver NPs. The colors of wool fabrics altered with the morphologies of silver NPs. These modified wool fabrics were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that anisotropic silver NPs were effectively assembled on the surface of wool fibers when the solution pH and temperature was about 4 and 40°C, respectively. This assembling of silver NPs on the wool fibers was realized by the electrostatic interaction between wool fibers and silver NPs. This technique was also applied to gold NPs. The fabrics treated with anisotropic silver NPs showed high antibacterial activity against the bacteria of Escherichia coli. This study opens a new approach to color and functionalize conventional textile materials.

Polycyanurate nanorod arrays for optical-waveguide-based biosensing

We demonstrate high-sensitivity biosensing by optical waveguide spectroscopy (OWS) at visible wavelengths using aligned polycyanurate thermoset nanorods (PCNs) arranged in extended arrays as waveguides. The PCNs formed by thermal polymerization of a cyanate ester monomer in self-ordered nanoporous alumina templates were 60 nm in diameter and 650 nm in length. Subtle refractive index changes of the medium surrounding the nanorods could be detected by monitoring the angular shifts of waveguiding modes. The sensing figure of merit thus achieved amounted to 196 reciprocal refractive index units and is, therefore, higher than that of other sensors based on angular modulation, while the configuration used here is eligible for further surface functionalization. Kinetics of the binding of taurine to the surface cyanate groups of the PCNs was monitored by OWS. Thus, modified PCNs bearing sulfonic acid groups at their surfaces were obtained. PCN arrays may represent a versatile platform for the design of biosensors.

Probing a century old prediction one plasmonic particle at a time

In 1908, Gustav Mie solved Maxwell's equations to account for the absorption and scattering of spherical plasmonic particles. Since then much attention has been devoted to the size dependent optical properties of metallic nanoparticles. However, ensemble measurements of colloidal solutions generally only yield the total extinction cross sections of the nanoparticles. Here, we show how Mie's prediction on the size dependence of the surface absorption and scattering can be probed separately for the same gold nanoparticle by using two single particle spectroscopy techniques, (1) dark-field scattering and (2) photothermal imaging, which selectively only measure scattering and absorption, respectively. Combining the optical measurements with correlated scanning electron microscopy furthermore allowed us to measure the size of the spherical gold nanoparticles, which ranged from 43 to 274 nm in diameter. We found that even though the trend predicted by Mie theory is followed well by the experimental data over a large range of nanoparticle diameters, for small size variations changes in scattering and absorption intensities are dominated by factors other than those considered by Mie theory. In particular, spectral shifts of the plasmon resonance due to deviations from a spherical particle shape alone cannot explain the observed variation in absorption and scattering intensities.

In situ investigation of Pt(100--x)Au(x) and Pt(100--y)Sn(y) nanoalloys

Dispersed sols of 1-10 nm sized Pt(100--x)Au(x) and Pt(100--y)Sn(y) nanoalloys have been prepared separately at various x and y above and below the miscibility limit in the bulk metals. Pt(100--x)Au(x) was derived from trisodium citrate reduction of aqueous solutions of H2PtCl6 and HAuCl4. Pt(100--y)-Sn(y) was produced by (i) complexing Sn2+ with glucose at 323 K at pH > 7, (ii) neutralising this with H2PtC16 addition and (iii) reducing the bimetallic precursor with glucose on raising the temperature to 373 K. For Pt(100--x)Au(x (where both metals were zero-valent) as x increased the average size of nanoalloy particles increased. These particles adsorbed onto graphite, where the extent of hydrogen chemisorption at 298 K decreased by 67% at 9 at % Au. Pt/SnO2 nanoparticles (<3 nm in size) were adsorbed onto alumina. The Pt interacted with and catalysed the reduction of SnO2, with some Pt(100--y)Sn(y) nanoalloy formation at about 673 K which even in the bulk occurs over a wider range of compositions than Pt-Au) and enhanced H2 chemisorption at 17-33 at % Sn. Nevertheless some Sn must remain in a positive oxidation state on the alumina surface. The ratio of rates of 2MP/ 3MP formation from MCP and n-hexane may be informative in chemically fingerprinting (and revealing fundamental differences in) these nanoalloy surfaces. The reasons for this are seen in terms of the surface structures on these two types of nanoalloy particles (i.e. the availability of contiguous asymmetric pairs of active surface atoms *, which, as expected, is found to pass through a maximum or decrease beyond specific values of x and y).