Spectroscopy, interactions, and level splittings in an nanoparticles

We have measured the electronic energy spectra of nm-scale Au particles using a new tunneling spectroscopy configuration. The particle diameters ranged from 5 to 9 nm, and at low energies the spectrum is discrete, as expected by the electron-in-a-box model. The density of tunneling resonances increases rapidly with energy, and at higher energies the resonances overlap forming broad resonances. Near the Thouless energy, the broad resonances merge into a continuum. The tunneling resonances display Zeeman splitting in a magnetic field. Surprisingly, the a factors (similar to 0.3) of energy levels in Au nanoparticles are much smaller than the g factor (2.1) in bulk gold.