Ballistic Electron Emission Spectroscopy Studies of Gold Nanocrystals

We report experimental measurements of ballistic electron emission spectroscopy (BEES) on single gold nanocrystals. Nanocrystals with core diameters from 1 nm to 3 nm were chemically attached to a 10-nm thick gold film that was vapor-deposited on a silicon substrate. Low temperature (77 K) scanning tunneling microscopy and spectroscopy were used to image and identify nanocrystals prior to BEES measurements. A comparison of BEES spectra acquired by tunneling through a nanocrystal with those acquired by tunneling directly to the gold film, shows attenuation of the BEES signal by a factor of typically 4-10. From a simple rate equation, electron relaxation times in these gold nanocrystals are estimated to be of order 10 picoseconds.