Reflection of light by metal nanoparticles at electrodes.

We present model calculations for the reflection spectrum of an ordered two dimensional array of metallic nanoparticles located near an electrochemical interface. We consider three cases, nanoparticles at: (i) a metal electrode, (ii) a transparent semiconductor electrode, and (iii) an electrified liquid/liquid interface. In the case of a metal electrode, the presence of nanoparticles introduces dips in reflection, whose position and depth are affected by the distance and size of the nanoparticles. For both a transparent semiconductor electrode and a liquid/liquid interface, the presence of nanoparticles enhances reflectivity. The spectra are sensitive to the particle spacing and size. The response from all three systems exhibits a strong dependence on the polarisation of light. The dependence on the angle of incidence reveals shallow dips typical of surface plasmon resonance spectra. These findings suggest diagnostic tools for the detection and characterisation of nanoparticle monolayers on functionalised electrodes, and enable electrovariable optical devices based on the controlled assembly of nanoparticles at interfaces.