Département de Chimie Physique , Université de Genève, Quai Ernest-Ansermet
30, CH-1211 Genève 4, Switzerland. Two principle structures studied:.
Département de Chimie Physique , Université de Genève, Quai Ernest-Ansermet 30, CH-1211 Genève 4, Switzerland Introduction & Background
Results – Core-shell nanoclusters
Physical chemistry group that bring the following areas of expertise to the project: •Analogous system on SiO2 spheres can be fabricated in solution or as part of an array on a planar substrate (Figures 3 and 4).
•Metallic nanoparticle fabrication •Bottom-up organisation of metallic nanoparticles into larger assemblies •Spectroscopic characterisation (UV-Vis, ATR-IR, PMIRRAS)
• Theoretical studies show similar organisations of metallic nanoparticles induce a magnetic dipole moment and could support negative refractive indices.[2], [3] 100 nm
Overview Two principle structures studied: •Large scale layered arrays of strongly coupled gold nanoparticles (GNPs) •Control over a number of material parameters (composition, size, shape, interlayer separation, inter-particle distance)
•Core-shell nanoclusters Figure 3. (left) – Diagrammatical representation of core-shell nanocluster showing induced magnetic dipole moment. (right) – SEM micrograph of isolated core-shell nanocluster.
•Proposed double negative properties
Results – Layered GNP arrays • GNPs and PE layers are deposited on functionalised substrates using electrostatic interactions (Figure 1). • Number of PE layers tunes distance and therefore electromagnetic coupling between GNP arrays (Figure 2).[1] • Also have high degree of control over GNP size and inter-particle separation within one array.
Polymer layers
GNPs
100 nm
Glass substrate Figure 1. (left) – Diagrammatical representation of GNP arrays separated by PE layers. (right) – SEM micrograph of two GNP arrays separated by 31 PE layers. GNP radius = 10 nm.
Figure 4. (left) - SEM micrograph of array of core-shell clusters. (right) – Extinction cross-section of core-shell nanoclusters fabricated on planar substrate. SiO2 NP radius = 130 nm, GNP radius = 10 nm.
Conclusions • Extremely flexible systems to organise metallic nanoparticles developed. • High degree of control over a number of material parameters. •This allows tailoring of inter-particle coupling, and therefore optical properties. • These optical predictions.
properties
show
excellent
agreement
with
theoretical
Outlook Figure 2. (left) - Red-shift of surface plasmon peak as a function of GNP layer separation for GNP radius = 20 nm. (right) – Extinction cross-section of single GNP array (black) and GNP bilayer arrays with 11, 21 and 41 PE separating layers (green, blue, red respectively).
• Incorporation into optical devices • Eventually for use as bulk metamaterials in the visible range • Other possible applications of such structures include: • SERS substrates • Sensing devices
References [1] Cunningham, Mühlig, Rockstuhl and Bürgi J. Phys. Chem. C, 2011, 115, 8955 [2] Mühlig, Cunningham, Scheeler, Pacholski, Bürgi, Rockstuhl and Lederer ACS Nano, 2011, xxx, xxxx [3] Tretyakov and Simovski Physical Review B, 2009, 79, 045111
Acknowledgements Funded by the European Union’s Seven Framework Programme (FP7 2007-2013) under Grant Agreement n°228455 (NANOGOLD)
