Colloidal quantum dots (CQDs) are semiconductor nanoparticles that, due to their size (2-20 nm), fall in the quantum confinement regime. As such, they exhibit optical properties that can be continuously adjusted over a wide range of wavelengths, from the infrared to the ultraviolet. These objects are very good single photon sources at room temperature, capable of emitting photons one-by-one with high efficiency. Recently, diluted CQDs were integrated within electrical transport layers, allowing to observe electrically-injected single-photon emission. Nevertheless, the charge injection pathway is very complex in such devices involving a very large ensemble of CQDs, and brightness is very low as single photon purity is achieved by collecting photons from a very limited area. In this internship, we propose to use scanning tunneling electroluminescence microscopy (STLM) to probe electronic and optical properties of CQDs with nanoscale resolution, essentially realizing a true single-CQD LED inside a STM equipped with light collection optics. The goals are: (1) probe the local electronic density of state at the single CQD level using to tunneling spectroscopy, correlate such measurements with collected electroluminescence and with ensemble optical spectroscopy; (2) build a Hanbury-Brown and Twiss interferometer (HBT) and observe single photon emission excited by tunnel currents in single CQDs; (3) provide an accurate description of the charge injection mechanism.