Figure 1

Schematic of an electrotuneable FP interferometer comprised of negatively charged NPs and two parallel ITO electrodes in aqueous electrolyte. Electrodes can be polarized with respect to a reference electrode, not shown. The particles are confined within the cavity volume by membranes, not shown, permeable for the electrolyte solution, but not the NPs. (a) For strong positive electrode polarisation, NPs assemble along the ITO-water interface in densely packed arrays to form an FP-cavity; (b) for weak positive electrode polarisation, sparse layers of NPs are formed with reduced plasmon coupling and reflectivity; (c) for negative electrode polarisation, NPs remain dispersed in the bulk and do not exhibit any significant absorption or scattering of light (due to absence of collective plasmon resonance), allowing almost-complete transmittance of the incident light with negligible losses within the cavity.