The thermal decomposition of Fe(CO)(5), Cr(CO)(6), Mo(CO)(6), and W(CO)(6) on Ni(100) surfaces and under ultrahigh vacuum conditions was studied by using temperature programmed desorption and x-ray photoelectron spectroscopies. The initial adsorption of those metal carbonyls is mostly molecular at low temperatures, but complete decarbonylation to the naked metal takes place in all cases upon thermal activation. Experiments with coadsorbed isotopically labeled (CO)-C-13 provided indirect evidence for a stepwise mechanism for Fe(CO)(5) which may include the formation of tetra- and tricarbonyl intermediates on the surface. For Cr(CO)(6), Mo(CO)(6), and W(CO)(6), on the other hand, complete decomposition occurs in a narrow range of temperature, and no intermediate could be isolated on the surface. The deposition of metal films via metal carbonyl activation was studied under steady state conditions as well. Continuous deposition was seen at substrate temperatures as low as 300 K, but the grown films were found to incorporate both carbon and oxygen under most conditions tested and to change their morphology depending on the substrate temperature during deposition.