Breaking and restoring a molecularly bridged metal|quantum dot junction

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. (C) 2002 American Institute of Physics.