Plasmon Controlled Shaping of Metal Nanoparticle Aggregates by Femtosecond Laser-Induced Melting.

In this work, we show how to control the morphology of femtosecond laser melted gold nanosphere aggregates. A careful choice of both laser fluence and wavelength makes it possible to selectively excite different aggregate substructures to produce larger spherical nanoparticles, nanorods, and nanoprisms or necklace-like 1D nanostructures in which the nanoparticles are interlinked by bridges. Finite integral technique calculations have been performed on the near-field concentration of light in the nanostructures which confirm the wavelength dependence of the light concentration and suggest that the resulting localized high intensities lead to nonthermal melting. We show that by tuning the wavelength of the melting light it is possible to choose the spatial extension of the ensembles of NPs heated thus allowing us to exhibit control over the morphology of the nanostructures formed by the melting process. By a proper combination of this method with self-assembly of chemically synthesized nanoparticles, one can envisage the development of an innovative high-throughput high-resolution nanofabrication technique.

Silica diatom shells tailored with Au nanoparticles enable sensitive analysis of molecules for biological, safety and environment applications.

Diatom shells are a natural, theoretically unlimited material composed of silicon dioxide, with regular patterns of pores penetrating through their surface. For their characteristics, diatom shells show promise to be used as low cost, highly efficient drug carriers, sensor devices or other micro-devices. Here, we demonstrate diatom shells functionalized with gold nanoparticles for the harvesting and detection of biological analytes (bovine serum albumin-BSA) and chemical pollutants (mineral oil) in low abundance ranges, for applications in bioengineering, medicine, safety, and pollution monitoring.

Hot-electron nanoscopy using adiabatic compression of surface plasmons.

Surface plasmon polaritons are a central concept in nanoplasmonics and have been exploited to develop ultrasensitive chemical detection platforms, as well as imaging and spectroscopic techniques at the nanoscale. Surface plasmons can decay to form highly energetic (or hot) electrons in a process that is usually thought to be parasitic for applications, because it limits the lifetime and propagation length of surface plasmons and therefore has an adverse influence on the functionality of nanoplasmonic devices. Recently, however, it has been shown that hot electrons produced by surface plasmon decay can be harnessed to produce useful work in photodetection, catalysis and solar energy conversion. Nevertheless, the surface-plasmon-to-hot-electron conversion efficiency has been below 1% in all cases. Here we show that adiabatic focusing of surface plasmons on a Schottky diode-terminated tapered tip of nanoscale dimensions allows for a plasmon-to-hot-electron conversion efficiency of ∼30%. We further demonstrate that, with such high efficiency, hot electrons can be used for a new nanoscopy technique based on an atomic force microscopy set-up. We show that this hot-electron nanoscopy preserves the chemical sensitivity of the scanned surface and has a spatial resolution below 50 nm, with margins for improvement.