MECHANISMS OF CARBON AND OXYGEN INCORPORATION INTO THIN METAL FILMS GROWN BY LASER PHOTOLYSIS OF CARBONYLS

Two series of experiments were performed to study the deposition of metal films grown by laser photolysis of metal carbonyls. First, small-area Cr, Mo, and W films were grown by UV laser photolysis of Cr(CO)(,6), Mo(CO)(,6), and W(CO)(,6), respectively, and subsequently characterized. Elemental depth profiling by Auger electron spectroscopy revealed the presence of large amounts of oxygen in all of the films, with additional significant carbon contamination in the Mo and W films. Thermal and laser annealing of the films resulted in a reduction of the oxygen concentration.; Second, ultrahigh vacuum studies of the interaction of 257 and 514 nm radiation with mono- and multilayer coverages of Cr(CO)(,6), Mo(CO)(,6), and W(CO)(,6) adsorbed on Si(111)7 x 7 using thermal desorption spectroscopy, high resolution electron energy loss spectroscopy, laser induced desorption, and Auger electron spectroscopy were performed. These experiments were able to distinguish between photoelectronic and thermal effects in the decomposition and desorption mechanisms of the adsorbed carbonyls. The decomposition of adsorbed Mo(CO)(,6) is due to electronic excitation from direct absorption of the 257 nm radiation. The same mechanism is active for adsorbed W(CO)(,6); however, in addition, new excitation mechanisms are opened up that lead to bonding changes in the molecule through electronic excitation with visible radiation. The photodecomposition products of the adsorbed carbonyls are found to be different from those of the gas phase decomposition products. The surface stabilizes the adsorbed carbonyls, preventing complete removal of all the CO ligands. Evidence of metal clustering was also observed in the adsorbed species after 257 nm irradiation. These experiments have suggested possible mechanisms for carbon and oxygen incorporation into the films grown in the first series of experiments.