The surface reaction mechanisms of beta-diketones on transition metal surfaces including applications to metal thermal chemical vapor etching and heterogeneous catalyst particle redispersion

The surface reaction mechanisms of three beta-diketones, hexafluoroacetylacetone, trifluoroacetylacetone and acetylacetone were each determined on clean and oxygen precovered Cu(210) and Ni(110) surfaces. All surface mechanisms were resolved through temperature-programmed desorption and Auger spectroscopy performed under ultra-high vacuum.;The two fluorinated beta-diketones etched Cu at low-temperature from an oxygen pre-covered Cu(210) surface. Cu(CF3COCHCOCF3) 2 desorbed at 425 K while Cu(CF3COCHCOCH3) 2 desorbed at 380 K. In both studies, carbon dioxide formed (in a reaction between the adsorbed C=O moiety and surface oxygen) and started desorbing around 500 K, thus, reducing the oxygen pre-covered surface. Subsequently, decomposition pathways appeared which were similar to those seen on the clean surface also above 500 K. Unfortunately, acetylacetone decomposed on the oxygen pre-covered surface before the etching activation barrier was surpassed and, therefore, did not dry etch Cu under these conditions. A possible polymerization pathway was observed for the two fluorinated beta-diketones on the clean Cu(210) surface below 300 K. Subsequent decomposition of this polymer resulted in some unusual desorption products and, above 600 K, significant surface carbon contamination.;All three beta-diketones etched Ni at low-temperature from an oxygen pre-covered Ni(110) surface. Ni(CF3COCHCOCF3)2 desorbed in two maximum rate desorption states at 380 K and 480 K. Ni(CF3COCHCOCH3)2 desorbed at 340 K and in a much less intense state at 420 K. Ni(CH3COCHCOCH3) 2 desorbed at 340 K. Etching ceased for all beta-diketones as the surface became reduced by the formation and desorption of carbon dioxide (by the same interaction noted on the Cu surface) around 500 K. Again, clean surface reaction pathways re-appeared. These were mostly beta-bond scission mechanisms that, above 600 K, resulted in surface carbon contamination. On the clean Ni(110) surface, a radical stabilization component of the decomposition and desorption mechanisms was also observed.;Interestingly, the metal-bis(tfac) and metal-bis(acac) chelates desorbed at lower temperatures than the metal-bis(hfac) chelates. The most fluorinated chelate is the most volatile and is expected to desorb at the lower temperature. This phenomenon indicates that there may be surface-reaction and desorption limitations to etching that increase with increasing ligand fluorination. Unfortunately, greater details concerning these surface reaction or desorption limitations to etching are not understood at this time.;Investigation of the interactions of beta-diketones was also done on alumina and gamma-alumina supported Pd catalysts in an attempt to alter Pd particle dispersion. Low-temperature redispersion of a sintered 5% Pd/gamma-alumina catalyst was most successful via exposure to oxygen and acetylacetone at ∼560 K for 8 hours. A bimodal distribution of CO desorption states was achieved, at 405 K and 585 K, with more CO desorbing from the high-temperature state. This indicated a decrease in Pd particle size relative to the sintered and, to some extent, untreated catalyst samples. Surface mechanisms were not investigated in this particular study.