  Using cryogenic scanning tunnelling microscopy and scanning tunnelling
spectroscopy we measured single electron tunnelling of isolated Au
nanoparticles with 1.4 nm in radius. We observe that a gap {\Delta}V ~ 2e/C (C
is the capacitance of the Au particle) around zero bias in the tunnelling
conductance spectrum, followed by a series of discrete single electron
tunnelling peaks with voltage widths of EC ~ e/C at both negative and positive
bias. Experimental data are well explained by taking into account the effect of
exchange interaction of electrons on the single electron tunnelling of Au
nanoparticles. A tunnelling peak near zero-bias was suppressed by the
exchange-type zero-bias anomaly, which results in the gap {\Delta}V ~ 2EC.
