THERMAL AND PHOTOINDUCED DECOMPOSITION OF W(CO)6 ON W(110)

The thermal and laser-induced decomposition of W(CO)6 adsorbed on W(110) was investigated under ultrahigh vacuum with temperature-programmed desorption/reaction, laser-induced decomposition, and Auger electron spectroscopy. Both thermal and photochemical decomposition processes are found to be fundamentally important to the process of film growth from W(CO)6. W(CO)6 decomposes at a temperature less than 200 K on clean W(110), yielding W(CO)(x) fragments and molecularly adsorbed CO. This thermal decomposition occurs until the surface is sufficiently covered with CO and W(CO)(x) fragments. Inhibition of thermal decomposition also can be accomplished by pre-deposition of CO or carbon and oxygen. The photochemical activity of multilayer W(CO)6 coverage is more efficient than submonolayer coverage. Thermal and photochemical W(CO)(x) fragments further decompose at a temperature around 250 K, and the CO evolved in this decomposition is observed to induce desorption of neighboring molecular CO. The resulting fragments still contain some CO from the parent W(CO)6 molecule, and desorption of CO from beta states is affected by the presence of the fragments. These surface-based mechanisms show that the purity of laser-induced film growth from W(CO)6 is inherently limited by both thermal decomposition and incomplete photoinduced decarbonylation.