STM visualization of local density of optical states of gold nanoantennas with sub-diffraction resolution

Simultaneous recording of luminescence induced by inelastic electron tunneling together with topography in scanning tunneling microscopy (STM-L) is a powerful tool in the study of local optical properties of nanostructures. In this study, we use the STM-L technique to visualize the local density of optical states (LDOS) by detecting the optical signal generated in the tunnel junction between a tungsten STM probe and a hollow hemispherical gold nanoantenna (d = 500 nm, h = 300 nm) fabricated by femtosecond laser printing. The light emission from the tunnel gap is caused by the process of inelastic tunneling of electrons. The intensity of photon signal directly dependent on LDOS — a key parameter in the design of light emitting inelastic tunneling-based nanoscale photon sources. We demonstrate that the STM-L method can provide information on the LDOS features of individual nanoantenna with sub-diffraction spatial resolution, as well as reveal smooth LDOS variations in periodic arrays of nanoantennas. These results highlight the unique capability of STM-L to reveal nanoscale optical patterns inaccessible to conventional diffraction-limited microscopy, highlighting its potential for advanced optical characterization at the nanoscale.