Metallic nanoparticles for plasmonic absorption enhancement (Vol. 45 No. 1)

Expected optical generation rate for a solar cell with integrated random nanoparticles assemblies as visible from the overlapped topography.

Random arrangements of nanoparticles are easy to fabricate and therefore find widespread application. But how do these random assemblies influence the local optical generation rate? The authors investigated Ag nanoparticle assemblies with scanning near-field optical microscopy (SNOM) detecting the optical response to local near-field excitation through an aperture tip while simultaneously recording the topography with atomic force microscopy. 3D simulations in finite-difference time domain confirmed that areas in between irregularly arranged nanoparticles show the strongest response and that no direct correlation of hot spots to particularly sized nanoparticles is possible. An overall highly non-uniform distribution of the electric field is found around the nanoparticles for various wavelengths both in experiment and theory. These variations in local electric field are expected to translate directly to the optical generation rate, which therefore will equally suffer from inhomogeneities (see figure), and will thus crucially determine the effectiveness of plasmonic absorption enhancement. Therefore mapping the local field distributions as possible with SNOM is expected to be highly advisory to optimize nanoparticle geometries.

M. Schmid, J. Grandidier and H. A. Atwater, “Scanning near-field optical microscopy on dense random assemblies of metal nanoparticles“, J. Opt., 15, 125001 (2013)