Optical Interference Substrates for Nanoparticles and Two-Dimensional Materials

Interference substrates are useful in enhancing Raman and luminescence signals and in increasing the optical contrast of nanoparticles and atomically thin layers. Interference substrates played a crucial role in the discovery of the electric field effect on electronic conduction in graphene a few years ago. They are now used for a wide range of two-dimensional materials and recently for the heterostructures of atomically thin films. The same or similar substrates can be employed for the exploration of a large variety of nanoparticles. Although optical interference has been known to occur within the proximity of surfaces for more than one century, optical interference has been only gradually used over the last two decades to enhance the optical response of nanoparticles and layered materials. We review the different forms of interference substrates used over time. While multiple interference effects are frequently put forward to explain the enhancement in interference substrates, we show here that the formation of optical surface standing waves near strongly reflecting surfaces is the main cause of field enhancement. In addition, we demonstrate how a metal layer improves optical field enhancement.