The tip of a scanning tunnelling microscope (STM) has been used to deposit nanometer-sized clusters of copper or silver on bare and thiol-covered gold electrode surfaces at predetermined positions. First, metal is deposited electrochemically onto the STM tip, then the clusters are formed by a jump-to-contact between the tip and the substrate during a short and very controlled approach of the tip towards the surface. When Ni is deposited onto the tip, the jump-to-contact occurs in the opposite direction leaving holes in the gold surface. The stability of the metal clusters against anodic dissolution is discussed. Finally, it is shown how the tip approach can be used to determine tunnel barriers at the metal-electrolyte interface.