Tunable Plasmonic Quantum Light Source with Silver Nanoclusters on a Silver Surface

Scanning tunneling luminescence (STL) can be used to investigate the optical properties of nano structures with high spatial resolution beyond the diffraction limit of light. To get appropriate STL spectra, one needs to modify the tip repeatedly. However, such irreversible tip modification often leads to very unstable tips. Here, by using a scanning tunneling microscope (STM) tip, we demonstrate that STL spectra are tunable via silver nanocluster arrays fabricated directly on a silver surface. The silver nanoclusters are created by transferring silver atoms from the silver tip to the silver surface under STM. We found that the STL spectra were enhanced (suppressed) at higher (lower) energy on the clusters and that they showed opposite behaviors between the nanoclusters. Without relying on the irreversible tip shape modification, our findings indicate that we can tune the STL spectra simply by moving the STM tip over the nanoclusters. Our method can be used to provide a tunable light source for systematic nano-optical experiments and for nanoscale optical devices.