Binary plasmonic honeycomb structures: High-resolution EDX mapping and optical properties

Significance Statement

Substrate supported lattices of metal nanoparticles with controlled inter-particle distances find applications in sensing, optical metamaterials, and plasmonic lasing. These structures are typically fabricated by top-down methods using lithography, for instance, ion-beam, beam or UV photolithography providing nanostructures with dimensions down to a few nanometers. These methods further allow for the fabrication of periodic nanoarrays with controllable inter-particle distances and lattice symmetry. Apart from hexagonal and square lattices, honeycomb structures have gained significant attraction recently.

Researchers lead by Professor Matthias Karg from the Heinrich-Heine-University Düsseldorf in Germany (previous affiliation: University of Bayreuth, Germany), demonstrated the bottom-up preparation of binary plasmonic superstructures via an interface-mediated self-assembly route. The sequential double deposition of individual colloidal monolayers was employed to produce a honeycomb lattice with gold and silver nanoparticles at alternating positions. Their work in now published in the peer-reviewed journal, Colloids and Surfaces A: Physicochemical and Engineering Aspects.

Their experiments are based on noble metal-hydrogel core-shell particles that were prepared in a two-step protocol. In the first step, gold-hydrogel core-shell particles were synthesized by  seeded precipitation polymerization of N-isopropylacrylamide in presence of a chemical cross-linker (N,N’-methylenebisacrylamide). In the second step, the gold nanoparticle cores of these core-shell particles were selectively overgrown either by gold or by silver. This growth resulted in [email protected] particles with cores of a total diameter of 75 nm and [email protected] particles with 99 nm total core diameter. Due to the use of the same starting material, the overall hydrodynamic dimensions of the two systems are identical. In order to fabricate highly ordered, non-close packed, plasmonic monolayers from these building blocks, the authors used interface-mediated colloidal self-assembly. When immersed at the air/water interface, both core-shell systems formed homogeneous, macroscopic monolayers spontaneously. Upon transfer of the freely floating monolayers onto solid supports such as microscopy glass slides or TEM grids, substrate supported hexagonally ordered colloidal monolayers were obtained. Investigating the monolayer structure by different microscopy techniques revealed an extraordinary high degree of order with large, single-crystalline domains for both types of core-shell particles. Due to the hydrogel shells – acting as a semitransparent spacer – the metal nanoparticle cores were well-separated with average center-to-center inter-particle distances close to 500 nm.

As the key experiment the authors demonstrated a sequential double deposition of monolayers from the [email protected] and the [email protected] core-shell particles. This way binary plasmonic honeycomb lattices were created. The extinction of the binary lattice revealed a broad plasmon resonance with the indication of plasmon resonance coupling between the metal cores. Through EDX mapping the authors were able to distinguish between positions of the silver and gold cores. They found that the center-to-center distances in  each of the hexagonal sublattices were 470 nm. This was a close match todistances of the individual single monolayers. The center-to-center distance between silver and gold particles in the resulting binary honeycomb lattice was 271 nm.

Binary plasmonic honeycomb structures High-resolution EDX mapping - Advances in Engineering

About The Author

Tobias Honold is currently a Ph.D. student in the Physical Chemistry I department of the University of Bayreuth. He studied Polymer and Colloid Science as an undergraduate at the University of Bayreuth. Following this, he obtained his Master’s degree in Polymer Science in 2013 from the same university.

His current research interests address the fields of nanophotonics and plasmonics, including surface modification of nanoparticles, self-assembly of soft core-shell particles, and plasmonic optoelectronic devices.

About The Author

Kirsten Volk is currently a Ph.D. student in the Physical Chemistry I department of the Heinrich-Heine-University Düsseldorf. As an undergraduate she studied Polymer and Colloid Science and obtained a Master’s degree in Polymer Science in 2014 from the University of Bayreuth.

Her current research interest lies in the field of plasmonics, including nanoparticle synthesis, encapsulation, self-assembly into plasmonic lattices, optical tunability of plasmonic devices as well as energy-transfer-processes of those assemblies with gain media.

About The Author

Markus Retsch studied Polymer- and Colloid Chemistry at the University of Bayreuth (Germany) from 2001 – 2006. He received his Ph.D. degree from the Max Planck Institute for Polymer Research/University of Mainz (Germany) in 2009. Following a postdoctoral stay at the Massachusetts Institute of Technology (MIT, USA) from 2009 – 2011, he was appointed Junior-Professor at the University of Bayreuth (Germany). In 2013 he received a Lichtenberg professorship provided by the Volkswagen foundation, and in 2016 he was awarded an ERC starting grant.

The Retsch group focuses on functional colloidal materials with a particular interest in energy conversion and energy conservation technologies. Topics of interest are colloidal self-assembly processes, thermal transport in nano- and mesostructured materials, broadband nanophotonic engineering and plasmonic superstructures and their relevance for photovoltaic applications.

About The Author

Matthias Karg studied chemistry at the TU Berlin (Germany) from 2001 to 2006. He received his Ph.D. degree from the same university in 2009. Afterwads he joined the University of Melbourne (Australia) as a postdoctoral research fellow funded by the Alexander von Humboldt foundation (Feodor Lynen programme) until 2011. He then returned to Germany to work as a junior professor in Physical Chemistry at the University of Bayreuth. Since 2016 he is working as a full professor chairing the Physical Chemistry I department of the Heinrich-Heine-University Düsseldorf (Germany). Since 2013 he leads an Emmy Noether reserach group funded by the German Research foundation (DFG).

The Karg group is interested in a broad range of topics in the field of colloid and polymer science. In particular, we study the self-assembly of soft colloidal building blocks, energy-transfer processes between plasmonic and gain materials, optical phenomena at the nanoscale as well as new responsive polymer systems.

Journal Reference

Tobias Honold1, Kirsten Volk1, Markus Retsch2, and Matthias Karg1,3. Binary plasmonic honeycomb structures: High-resolution EDX mapping and optical properties. Colloids and Surfaces A: Physicochem. Eng. Aspects, volume 510 (2016), pages 198-204.

Show Affiliations
  1. Physical Chemistry − Colloidal Systems, University of Bayreuth, Universitaetsstr. 30, 95440 Bayreuth, Germany.
  2. Physical Chemistry − Polymer Systems, University of Bayreuth, Universitaetsstr. 30, 95440 Bayreuth, Germany.
  3. Physical Chemistry I, Heinrich-Heine-University Duesseldorf, Universitaetsstr. 1, 40225 Duesseldorf, Germany.

 

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