Influence of the Tip Shape on Scanning Tunneling Luminescence Spectra: Implications for Nanomaterial Characterization

Scanning tunneling luminescence (STL) provides a unique opportunity to determine the optical properties of nanostructures beyond the diffraction limit. However, the relationship between the STL spectra and nanoscale tip shapes remains poorly understood because of the uncertainty regarding the nanoscale tip geometry. Here, we provide direct experimental evidence supporting a relationship between the tip shapes and resulting STL spectra. We find that asymmetric nanoscale tips generated dissimilar STL spectra in different directions by simultaneously collecting STL spectra in two opposing directions. Our experiment provides an efficient way to tune the STL spectra, which can be used to characterize the optical properties of nanomaterials.