Ultrafast Dynamics of Photoexcited Hot Carrier Generation and Injection in AgNWs@TiO₂@GNS Nanostructures

The generation and injection of hot electrons in plasmonic nanostructures have received a wide-range potential application in the next generation of ultrafast nanophotonics as well as energy harvesting, storage and conversion. In many cases, the energetic carriers with high energy beyond Fermi level are desirable for photochemical reactions due to the tremendous efficient hot electron injection. However, directly electron–electron scattering lifetime observations have few reported and hot electrons generally suffer from a low generation efficiency in conventional plasmonic nanostructures. This paper reports on the fabrication of hybrid AgNWs@TiO₂@Au core–shell nanostructures and the investigation of the ultrafast dynamics of their energetic carriers based on interband and intraband excitations through transient absorption spectroscopy measurements. Finally, the different electronic transition processes are discussed in terms of ultrafast decay response, which is necessary to design proper nanostructures aimed at efficient hot electron injection

EPR and Rheological Study of Hybrid Interfaces in Gold–Clay–Epoxy Nanocomposites

With the aim to obtain new materials with special properties to be used in various industrial and biomedical applications, ternary “gold–clay–epoxy” nanocomposites and their nanodispersions were prepared using clay decorated with gold nanoparticles (AuNPs), at different gold contents. Nanocomposites structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Rheology and electron paramagnetic resonance (EPR) techniques were used in order to evaluate the molecular dynamics in the nanodispersions, as well as dynamics at interfaces in the nanocomposites. The percolation threshold (i.e., the filler content related to the formation of long-range connectivity of particles in the dispersed media) of the gold nanoparticles was determined to be ϕ_p = 0.6 wt % at a fixed clay content of 3 wt %. The flow activation energy and the relaxation time spectrum illustrated the presence of interfacial interactions in the ternary nanodispersions around and above the percolation threshold of AuNPs; these interfacial interactions suppressed the global molecular dynamics. It was found that below ϕ_p the free epoxy polymer chains ratio dominated over the chains attracted on the gold surfaces; thus, the rheological behavior was not significantly changed by the presence of AuNPs. While, around and above ϕ_p, the amount of the bonded epoxy polymer chains on the gold surface was much higher than that of the free chains; thus, a substantial increase in the flow activation energy and shift in the spectra to higher relaxation times appeared. The EPR signals of the nanocomposites depended on the gold nanoparticle contents and the preparation procedure thus providing a fingerprint of the different nanostructures. The EPR results from spin probes indicated that the main effect of the gold nanoparticles above ϕ_p, was to form a more homogeneous, viscous and polar clay–epoxy mixture at the nanoparticle surface. The knowledge obtained from this study is applicable to understand the role of interfaces in ternary nanocomposites with different combinations of nanofiller

Chiral Colloids: Homogeneous Suspension of Individualized SiO₂ Helical and Twisted Nanoribbons

Finely tuned chiral nanometric silica fibers were synthesized based on sol–gel chemistry using organic self-assembly as a template. The optimization of the sol–gel process in acidic conditions allowed us to reduce the transcription time by a factor of 10. These nanohelices were successfully fragmented while preserving the fine internal structures from several micrometers to several hundreds of nanometers in length by a sonication method previously reported for carbon nanotubes. By carefully choosing the nature of the solvent, the sonication power, pH in the case of water, and densification of the silica walls by freeze-drying, the homogeneous and stable colloidal suspensions of individualized chiral nanometric silica ribbons with controlled length were obtained