Bridging Plasmonic Properties to Materials

Abstract:

Plasmonic nanoparticles resonantly couple light to matter, confining electromagnetic fields into spatial regions below the diffraction limit, potentially enabling disruptive optical materials with applications ranging from energy harvesting, to light sources, and in nanomedicines. However, developing approaches to control the nanometer sized elements while simultaneously enabling macroscale throughput has remained challenging and is critical in transitioning these novel properties to materials. Here I will highlight recent work in my group developing device-scale plasmonic nanostructures using directed self-assembly approaches.

As the miniaturization of devices continues down to nanometer length scales, the need to sense and signal using nanoantennae is paramount. I will discuss a generalized approach to solve the longstanding issue of efficiently creating nanoantennae by ‘gluing’ small aspect ratio gold nanorods together end to end with molecular linkers forming linear chains and ‘welding’ the chains together upon exposure to femtosecond laser pulses, producing trillions of infrared plasmonic nanoantennae per minute. Experiments demonstrate tuning ranges of over 2,000 nm from visible to infrared wavelengths.

Generally, plasmonic materials have been limited to only a few phases of matter, either as 2D solids or dilute liquids. Here, I introduce a novel phase of plasmonic matter, a plasmonic aerosol, by transitioning liquid suspensions of gold nanorods into the gas phase and simultaneously measuring their optical spectra. By measuring and modeling the evolution of the longitudinal absorbance peak of the nanorods from the liquid to the gas phase, we find that the aerosols are optically homogeneous and thermodynamically stable. For high aspect ratio nanorods the sensitivity becomes extremely large, which may be useful in aiding geoengineering challenges.  

Liquid crystal based devices can dynamically control the properties of light, which has enabled flat screen televisions and smart phone technologies. Yet, the Achilles heel of these devices are their slow, millisecond switching speeds, constraining potential applications. I will introduce the concept of a dynamic plasmonic pixel as a novel paradigm for liquid crystal devices using the electric field controlled alignment of gold nanorods, demonstrating switching times at least 1000x faster than a traditional Freederickcz-based liquid crystal alignment mechanism.

Finally, classical theory predicts the local field enhancement becomes infinite as the interparticle gap between the nanoparticles approaches zero, which is physically impossible, therefore breakdown of the field must occur. To probe this limit, centimeter-scale area metasurfaces were created composed of a hexagonally close packed monolayer of gold nanospheres coated with alkanethiol ligand shells, with tunable sub-nm interparticle gaps. Experiments show that the optical response of the metasurfaces agrees well with a classical model, with only small nonlocal effects, for gaps comparable to the atomic lattice length of gold. Consequently, experiments determined the dispersion of the effective real part of the refractive index ranged from 1.0 to 5.0.

Biography:

Dr. Fontana is a Research Physicist in the Center for Bio/Molecular Science and Engineering at the Naval Research Laboratory in Washington, D.C.. He earned his bachelor degree in physics from the California Polytechnic University in 2004 and his Ph.D. in chemical physics from the Liquid Crystal Institute in 2011. He was awarded a National Research Council Postdoctoral Associateship at the Naval Research Laboratory in 2011. In 2013 he was hired as a Jerome and Isabella Karle Distinguished Fellow at the Naval Research Laboratory. Dr. Fontana’s research programs lie at the interface between physics, chemistry and biology. His research is primarily focused on developing ‘soft’ nanocomposites with unique optical properties and transitioning these properties to functional materials