Aluminum nanostructures for UV plasmonics

Progress in nanomedicine will be driven by the ability to detect and manipulate the living matter at the molecular scale in order to cure cancers or fix genetic anomalies. One of the most promising way is the use of confined optical source in the ultra-violet wavelengths to image by self fluorescence, to analyse by enhanced Raman spectroscopy and to repair the wrong molecular sequences by inducing local chemical reaction. Metallic nanoparticles are widely recognized as local sources of energy that resolve the above issues thanks to their optical properties based to the plasmon resonance. To achieve UV plasmonics, aluminum appears as the best candidate. This metal has a negative dielectric constant combined with a low loss coefficient at UV wavelengths down to 100 nm, matching all the criteria to obtain high energy Localized Surface Plasmon Resonances (LSPR). UV Localized Surface Plasmon Resonances (LSPRs) are very attracting because their energy matches with most of the electronic transition energies of molecules or solids. In this scope, the development of efficient and low-cost techniques for the synthesis of reproducible Al nano-structures with very good crystalline quality and optical properties has to be investigated. In this presentation, we describe various methods for the growth of crystalline Al-NPs. The nanoparticles are made using very reproducible synthesis routes. The first approach is based on the reduction of aluminum ions. The second approach relies on the use of sono-chemistry of aluminum foils. Particles as small as 2nm have been synthesized and characterized with a transmission electron microscope, extinction spectroscopy and other methods. By playing on various the medium of synthesis and the temperature of reaction, it appears to be possible to tune under control the size of the nanoparticles. We completed the characterizations by investigating the optical properties of the synthesized Al NPs. Extinction measurements were performed on different solutions containing Al NPs using a UV-visible spectrometer. Sharp extinction peaks appear unveiling LSPR excitations of Al NPs. The relatively low FHWM of the LSPR peak indicates a good homogeneity of the NPs size as it has been verified by the TEM characterizations. Furthermore, it appears that the alumina shell is tremendously photoluminescent, thus paving the way for numerous applications as nano markers... To summarize, we described in this presentation various chemical method for the growth of aluminum nanoparticle. AL-NPs present a very good homogeneity and reproducibility. They exhibit sharp localized surface plasmon resonances (LSPRs) in the UV region as it has been showed by extinction spectroscopy characterization.