Quantum capacitance of a nanojunction

The capacitance of a nanojunction fromed by a scanning tunneling microscope (STM) tip and a two-dimensional gold cluster was measured through single electron tunneling spectroscopy of a double-barrier tunnel junction. By decreasing the STM tip-cluster separation, it was observed that the capacitance first increased and then decreased at short separation. This differs from classical behavior and provides evidence of quantum effects of the capacitance.