Breaking and restoring a molecularly bridged metal|quantum dot junction

Abstract

Nanometer-sized insulating quantum dots (CdSe and ZnO) have been attached to a Au(111) substrate, using molecular bridges with thiol and carboxylate end functions. We demonstrate that the quantum dots can be probed by a scanning tunneling microscope at negative substrate bias. At positive bias, however, the gold–sulfur bond is broken and the quantum dots are transferred to the tip. Individual CdSe quantum dots can be picked up by the tip and displaced on the substrate in a controlled way.