Nanocrystals can behave as quantum boxes with confined electronic states
governing their optoelectronic properties. The formation of nanometer-size
crystals of copper nitride (Cu3N) grown by nitrogen sputtering of a Cu(110)
surface is reported. Scanning tunneling spectroscopy shows that the
nanocrystals exhibit a series of well-defined sharp electronic resonances,
which correspond to confined free-electron-like states. We observe that
electrons from a scanning tunneling microscope tip induce the emission of
light with a larger efficiency than on the bare metal surface. The spectral
analysis of the emitted photons reveals various radiative inelastic pathways
enabled by the confined states, which explain the enhanced light emission.
Thus, the Cu3N nanocrystals can be employed as nanometer-size light sources.