Template-Free and Surfactant-Free Synthesis of Selective Multi-Oxide-Coated Ag Nanowires Enabling Tunable Surface Plasmon Resonance

Without using templates, seeds and surfactants, this study successfully prepared multi-oxide-layer coated Ag nanowires that enable tunable surface plasmon resonance without size or shape changes. A spontaneously grown ultra-thin titania layer onto the Ag nanowire surface causes a shift in surface plasmon resonance towards low energy (high wavelength) and also acts as a preferential site for the subsequent deposition of various oxides, e.g., TiO₂ and CeO₂. The difference in refractive indices results in further plasmonic resonance shifts. This verifies that the surface plasma resonance wavelength of one-dimensional nanostructures can be adjusted using refractive indices and shell oxide thickness design.

Full spectrum core-shell phosphors under ultraviolet excitation

A YAG

Ce/MgY4Si3O13:Ce-Y2O3:Eu core-shell structure was designed and accomplished via a urea homogeneous precipitation method. The as prepared phosphors can emit photons with a broad range of wavelengths from 340 nm to 700 nm under excitation light of 330 nm. The internal quantum efficiency can reach up to 68%.

Giant Vesicles with Anchored Tiny Gold Nanowires: Fabrication and Surface-Enhanced Raman Scattering

Sensitivity and reproducibility are two major concerns to improve the performance and extend the range of practical applications of surface-enhanced Raman scattering (SERS). A theoretical report reveals that hot spots formed by gold nanoparticles with a tip-to-tip configuration would generate the maximum electric field enhancement because of the lightning rod effect. In our present study, we constructed a giant vesicle consisting of anchored tiny gold nanowires to provide a high density of sharp tip-to-tip nanogaps for SERS application. The tiny gold nanowires were directly grown and anchored onto the surfaces of polystyrene (PS) microspheres by a seed-mediated method. Then, the removal of PS microspheres by tetrahydrofuran led to the formation of the giant gold vesicles with hierarchical cage structures, providing the sharp tips and high density of hot spots for improving SERS performance. Compared with the nonwire structure (island and inhibited nanoparticle), giant gold vesicles with tiny wires showed a higher SERS enhancement factor (9.90 × 10⁷) and quantitative SERS analysis in the range of 10^-4 to 10^-7 M. In addition, the large-scale giant gold vesicle array on the silica substrate resulted in a high reproducibility of SERS signals with the variation of intensities less than 7.6%.

Gold-silver@TiO2 nanocomposite-modified plasmonic photoanodes for higher efficiency dye-sensitized solar cells

In the present investigation, gold-silver@titania (Au-Ag@TiO₂) plasmonic nanocomposite materials with different Au and Ag compositions were prepared using a simple one-step chemical reduction method and used as photoanodes in high-efficiency dye-sensitized solar cells (DSSCs). The Au-Ag incorporated TiO₂ photoanode demonstrated an enhanced solar-to-electrical energy conversion efficiency of 7.33%, which is ∼230% higher than the unmodified TiO₂ photoanode (2.22%) under full sunlight illumination (100 mW cm^-2, AM 1.5G). This superior solar energy conversion efficiency was mainly due to the synergistic effect between the Au and Ag, and their surface plasmon resonance effect, which improved the optical absorption and interfacial charge transfer by minimizing the charge recombination process. The influence of the Au-Ag composition on the overall energy conversion efficiency was also explored, and the optimized composition with TiO₂ was found to be Au₇₅-Ag₂₅. This was reflected in the femtosecond transient absorption dynamics in which the electron-phonon interaction in the Au nanoparticles was measured to be 6.14 ps in TiO₂/Au₇₅:Ag₂₅, compared to 2.38 ps for free Au and 4.02 ps for TiO₂/Au₁₀₀:Ag₀. The slower dynamics indicates a more efficient electron-hole separation in TiO₂/Au₇₅:Ag₂₅ that is attributed to the formation of a Schottky barrier at the interface between TiO₂ and the noble metal(s) that acts as an electron sink. The significant boost in the solar energy conversion efficiency with the Au-Ag@TiO₂ plasmonic nanocomposite showed its potential as a photoanode for high-efficiency DSSCs.

Structure and mechanism of the formation of core-shell nanoparticles obtained through a one-step gas-phase synthesis by electron beam evaporation

The structure of core-shell Cu@silica and Ag@Si nanoparticles obtained in one-step through evaporation of elemental precursors by a high-powered electron beam are investigated. The structure of the core and shell of the particles are investigated in order to elucidate their mechanisms of formation and factors affecting the synthesis. It is proposed that the formation of Cu@silica particles is mainly driven by surface tension differences between Cu and Si while the formation of Ag@Si particles is mainly driven by differences in the vapour concentration of the two components.

Facile synthesis of Au@TiO2 nanocomposite and its application as a photoanode in dye-sensitized solar cells

Au@TiO₂ nanocomposite materials were synthesized by a facile one-step chemical reduction method and employed as photoanodes in dye-sensitized solar cells.

Al2O3/yttrium compound core–shell structure formation with burst nucleation: a process driven by electrostatic attraction and high surface energy

A partial wet chemical route has been developed, in which aluminium oxide (Al₂O₃) nanoparticles in a Y(NO₃)₃ solution are induced to form a core–shell-structured yttrium aluminum garnet (YAG) precursor based on a burst nucleation synthesis.

Quantification and morphology studies of nanoporous alumina membranes: a new algorithm for digital image processing

A new mathematical algorithm is reported for the accurate and efficient analysis of pore properties of nanoporous anodic alumina (NAA) membranes using scanning electron microscope (SEM) images. NAA membranes of the desired pore size were fabricated using a two-step anodic oxidation process. Surface morphology of the NAA membranes with different pore properties was studied using SEM images along with computerized image processing and analysis. The main objective was to analyze the SEM images of NAA membranes quantitatively, systematically, and quickly. The method uses a regularized shock filter for contrast enhancement, mathematical morphological operators, and a segmentation process for efficient determination of pore properties. The algorithm is executed using MATLAB, which generates a statistical report on the morphology of NAA membrane surfaces and performs accurate quantification of the parameters such as average pore-size distribution, porous area fraction, and average interpore distances. A good comparison between the pore property measurements was obtained using our algorithm and ImageJ software. This algorithm, with little manual intervention, is useful for optimizing the experimental process parameters during the fabrication of such nanostructures. Further, the algorithm is capable of analyzing SEM images of similar or asymmetrically porous nanostructures where sample and background have distinguishable contrast.