The fabrication of metal-dielectric nanocomposite materials with plasmonic attributes attracts more interest in several applications such as photovoltaics, sensing, photonics or in the emerging field of nanogenerators. Plasmonic nanoparticle gratings in particular, have been observed to offer new detection methods for bio-sensing and can considerably enhance the detection sensitivity. They can also be used as holographic concentrators for new generation concentrated photovoltaics. Therefore, polymers, which act as host matrices, have a number of advantages with regards to processing, low cost, and optical transparency. Above all, they are appropriate for single-step nanofabrication methods including direct laser printing and in-situ photo-reduction.
Concerning light-controlled fabrication of organized assemblages of nanoparticles in polymer series, a number of methods have been adopted. One method entails the addition of previously synthesized nanoparticles in azobenzene-based photosensitive polymers that are extensively applied in the area of optical data storage and that can be structured under appropriate irradiation conditions. Some authors have also applied standard interferometry patterning method to structure polymer periodically by photo-isomerization, which initiates nanoparticle distribution.
Unfortunately, it has been found that in the case of gold nanoparticles, the polymer structuring attributes deteriorate rapidly when the nanoparticle concentration surpasses 0.1wt%. This therefore puts a limit on tuning the intrinsic optical attributes of the composites as well as the development of plasmon-resonance based applications. In addition, to curtail aggregation, surfactants must be blended at the nanoparticles’ surface.
Researchers let by professor Hamid Kachkachi and working at the PROMES laboratory of the CNRS and the University of Perpignan in France developed a new approach for the fabrication of organized assemblies of plasmonic nanoparticles. They have shown that it is possible to use a continuous laser irradiation at 473nm to undertake in-situ photo-reduction of metallic precursors in a polyvinyl alcohol thin film. An annealing process that allowed for nanoparticle growth and nucleation then followed the photo-reduction. The authors observed a considerable difference in Plasmonic nanoparticle gratings they obtained as compared to those obtained with laser printing. Their work is published in peer-reviewed journal, Journal of Materials Chemistry C.
Details of the experimental procedure:
The authors prepared polymer films doped with gold precursors through spin coating. The resulting films were then irradiated with an interference pattern produced by a laser interferometry. The light allowed for spatially controlled in-situ photo-reduction for the gold particles. They then annealed the specimens to produce the nanoparticle formation from the organized reduced gold atoms.
The researchers used gold chloride (HAuCl4.3H2O) as a metallic precursor and polyvinyl alcohol as a polymer. The solution they applied for spin coating was synthesized in two processes. In the first stage, the authors dissolved polyvinyl alcohol in water and the solution stirred to attain complete dissolution. They then dissolved the gold precursor in the polyvinyl alcohol solution to obtain a gold-polyvinyl alcohol composite after spin-coating.
Spatially tuned photo-reduction led to the formation of surface relief gratings initiated in the course of nanoparticle growth. Concomitant effects of plasmonic attributes of the nanoparticles and periodic surface and refractive index modulation, led to the plasmon enhanced diffraction efficiency. The nanoparticle gratings showed considerable enhancement of diffraction efficiency in the zone of plasmon resonance of gold nanoparticles.
The newly developed method adopted in study of Elie Nadal and colleagues was based on cost-effective and environmentally-friendly materials and entails straightforward fabrication methods. The laser patterning method adopted was appropriate for large-scale production of organized nanostructures. More precisely, it was possible to design diffractive optical materials with custom-made dispersion as well as plasmon-improved diffraction efficiencies.
Elie Nadal said “We believe that in-situ synthesis of nanoparticles in polymers under irradiation is a very powerful and affordable technique to design tailored plasmonic systems. We are currently working on a new approach based on concentrated solar irradiation, which is one of the main research areas in our lab, and that is very promising. Our recent results showed that these techniques are not only efficient for the synthesis of plasmonic nanoparticles, but could also be used to fabricate a whole range of material trough identical photo-reduction process, such as magnetic nanocomposite for example.”
E. Nadal, N. Barros, H. Gle´nat, J. Laverdant, D. S. Schmool and H. Kachkachi. Plasmon-enhanced diffraction in nanoparticle gratings fabricated by in situ photo-reduction of gold chloride doped polymer thin films by laser interference patterning. Journal of Materials Chemistry C, 2017, 5, 3553—3560.Go To Journal of Materials Chemistry C