Monolayer-protected clusters: Molecular precursors to metal films

Monolayer-protected clusters (MPCs) are used to prepare solid, continuous m etal films containing a single white metal or an alloy thereof. MPCs consis t of nanoscopic metal cores coated with monolayers of thiolate ligands. In one method, multilayer films of carboxylate-functionalized alkanethiolate M PCs are assembled using Cu2+ coordinative bridges. The MPC film can be ther mally decomposed at moderate temperature (<350 <degrees>C) to produce films of the core metal; the thiolate ligands escape as volatile disulfides. In another method, solutions of MPCs with alkanethiolate monolayers are cast o r painted onto substrates, followed again by thermolysis to produce films o f core metals. Films prepared from MPCs having metal alloy cores tend to ex hibit metal segregation. A third method uses electrochemical generation of iodide at a Pt electrode to destabilize the MPC monolayer, an action that e ffectively coats the electrode with Au. The metal films are analyzed by sty lus profilometry, atomic force microscopy, energy-dispersive X-ray analysis , X-ray photoelectron spectroscopy, scanning electron microscopy, and elect rochemistry.