Metal Nanoparticle-Decorated Silicon Nanowire Arrays on Silicon Substrate and their Applications

Herein, we report an efficient method to produce silver (Ag) nanoparticle-decorated silicon (Si) nanowire (NW) arrays on a pyramidal Si (P-Si) substrate by using a pure chemical method and rapid thermal annealing in different atmospheres. A metal-assisted chemical etching technique was used to produce vertical Si NW arrays on pyramidal Si. The etching was observed to be heavily dependent on the substrate type. On planar Si (100), the etching was observed to occur in a uniform manner. However, the etching rate was observed to increase from the top to the base of the Si pyramid. The Si NWs produced from P-Si have zig-zag sidewalls as observed from high-resolution transmission electron microscopy images. However, for the same oxidant concentration, Si NWs produced from planar Si (100) consist of straight and amorphous sidewalls. Local variation of oxidant concentration is responsible for the formation of different sidewalls. The substrates are both surface-enhanced Raman scattering (SERS) active and hydrophobic. The hydrophobicity is due to the dual scale of roughness contributed to by both pyramidal and NW structures. Finite-difference time-domain simulation shows that the gap between two Ag spheres and also the gap between Si NWs and Ag spheres contributed to SERS enhancement.

Pulse Electrodeposition of Palladium Nanoparticles onto Silicon in DMSO

The deposition of palladium nanoparticles (PdNPs) on the surface of n-Si (100) substrate by pulsed electrolysis in dimethyl sulfoxide (DMSO) solutions of Pd(NO3)2 was investigated. It has been shown that nonaqueous medium (DMSO) contributes the Pd (II) recovery at high cathode potential values avoiding side processes to occur. In combination with the pulse mode, this allows the deposition of spherical PdNPs with their uniform distribution on the silicon surface. We established that the main factors influencing the geometry of PdNPs are the value of the cathode potential, the concentration of palladium ions in solution, and the number of pulse-pause cycles. It is shown that with increasing Ecathode value there is a tendency to increase the density of silicon surface filling with nanoparticles. As the concentration of Pd(NO3)2 increases from 1 to 6 mM, the density of silicon surface filling with PdNPs and their average size also increase. We found that with increasing the number of pulse-pause cycles, there is a predominant growth of nanoparticles in diameter, which causes 2D filling of the substrate surface.

Controllable synthesis, formation mechanism, and enhanced microwave absorption of dendritic AgFe alloy/Fe3O4 nanocomposites

Dendritic AgFe alloy/Fe₃O₄ nanocomposites with tunable composition and size synthesized via a selective attachment and anisotropic growth exhibit enhanced microwave absorption.

Hydrophobic mediated growth of galvanic-nanobuds from germanium nanowires for a highly tunable SERS substrate

A SERS substrate is fabricated through a scalable process exhibiting suitable hotspot distribution, shelf life, tunability, and biological applications.

Annealing Induced Morphology of Silver Nanoparticles on Pyramidal Silicon Surface and Their Application to Surface-Enhanced Raman Scattering

This paper reports on a simple and cost-effective process of developing a stable surface-enhanced Raman scattering (SERS) substrate based on silver (Ag) nanoparticles deposited on silicon (Si) surface. Durability is an important issue for preparing SERS active substrate as silver nanostructures are prone to rapid surface oxidation when exposed to ambient conditions, which may result in the loss of the enhancement capabilities in a short period of time. Here, we employ the galvanic displacement method to produce Ag nanoparticles on Si(100) substrate prepatterned with arrays of micropyramids by chemical etching, and subsequently, separate pieces of such substrates were annealed in oxygen and nitrogen environments at 550 °C. Interestingly, while nitrogen-annealed Si substrates were featured by spherical-shaped Ag particles, the oxygen annealed Si substrates were dominated by the formation of triangular shape particles attached with the spherical one. Remarkably, the oxygen-annealed substrate thus produced shows very high SERS enhancement compared to the either unannealed or nitrogen annealed substrate. The hitherto unobserved coexistence of triangular morphology with the spherical one and the gap between the two (source of efficient hot-spots) are the origin of enhanced SERS activity for the oxygen-annealed Ag particle-covered Si substrate as probed by the combined finite-difference time domain (FDTD) simulation and cathodoluminesensce (CL) experiment. As the substrate has already been annealed in an oxygen environment, further probability of oxidation is reduced in the present synthesis protocol that paves the way for making a novel long-lived thermally stable SERS substrate.

Role of oxygen in wetting of copper nanoparticles on silicon surfaces at elevated temperature

Copper nanoparticles have been deposited on silicon surfaces by a simple galvanic displacement reaction, and rapid thermal annealing has been performed under various atmospheric conditions. In spite of the general tendency of the agglomeration of nanoparticles to lower the surface energy at elevated temperatures, our plan-view and cross-sectional transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis shows that the thermal oxidation of the copper nanoparticles and formation of cupric oxide (CuO) on silicon surfaces leads to wetting rather than agglomeration. In contrast, agglomeration has been observed when copper nanoparticles were annealed in a nitrogen environment. The lattice transformation from cubic Cu to monoclinic CuO, and hence the change in surface energy of the particles, assists the wetting process. The occurrence of wetting during the oxidation step implies a strong interaction between the oxidized film and the silicon surface.

Electrochemical Ostwald ripening and surface diffusion in the galvanic displacement reaction: control over particle growth

We could control the particle growth in the galvanic displacement reaction on amorphous Ge substrate by introducing reduced electron mobility and surface defects over crystalline Ge, where electrochemical Ostwald ripening has been observed.

Green fabrication of antibacterial polymer/silver nanoparticle nanohybrids by dual-spinneret electrospinning

Nanohybrids from waterborne polyurethane, poly(vinyl alcohol) and silver nanoparticles of ultrasmall sizes (5.1 ± 0.6 nm) are facilely obtained by directly one-step dual-spinneret electrospinning fabrication in water without additional chemicals.

Nonidentical intracellular drug release rates in Raman and fluorescence spectroscopic determination

Intracellular drug release rates were measured by monitoring mitoxantrone (MTX) on gold nanoparticle (AuNP) carriers by means of real-time label-free bimodal imaging with confocal Raman and fluorescence spectroscopy. The quenching nature of the MTX-AuNPs by nanometal surface energy transfer (NSET) was analyzed using the determined Stern-Volmer constant of KSV = 2.28 × 10(9) M(-1). The amount of MTX released was estimated by both the decrease in the surface-enhanced resonance Raman scattering (SERRS) signal and the increase in the fluorescence intensity. Both SERRS and NSET provide quantitative relationships between the spectral intensities of MTX concentrations in solution. Inside live cells, the signal decay profiles of the drug release from AuNPs appeared to be faster at the beginning of the bond-breaking drug release for the SERRS (R(-12)) than the recovery time of the NSET (R(-4) or R(-6)). In the first 45 min, a rather fast decay rate k of 0.0252 min(-1) with a short half-life t1/2 of 27.5 min was observed, whereas the rate became significantly slower in a diffusion process, 0.0093 min(-1) with a longer half-life of 101.4 min, after 45 min.