PNNL

Abstract

The chemistry of Cr(CO)6 on the Fe3O4(111) surface termination of a-Fe2O3(0001) was explored using temperature programmed desorption (TPD), Auger electron spectroscopy (AES), static secondary ion mass spectrometry (SSIMS) and low energy electron diffraction (LEED) both with and without activation from an oxygen plasma source. No thermal decomposition of Cr(CO)6 was detected on the surface in the absence of O2 plasma treatment, with first layer molecules desorbing in TPD at 215 K from a close-packed overlayer. The interaction of first layer Cr(CO)6 with the Fe3O4(111)-termination was weak, desorbing only ~30 K above the leading edge of the multilayer state. Activation of multilayer coverages of Cr(CO)6 with the O2 plasma source at 100K resulted in complete conversion of the outer Cr(CO)6 layers, presumably to a disordered Cr oxide film, with Cr(CO)6 molecules near the surface left unaffected. Absence of CO or CO2 desorption states suggests that all carbonyl ligands are liberated for each Cr(CO)6 molecule activated by the plasma. AES and SSIMS both show that O2 plasma activation of Cr(CO)6 results in a carbon-free surface (after desorption of unreacted Cr(CO)6). LEED, however, shows that the Cr oxide film is disordered at 600 K and likely O-terminated based on subsequent water TPD. Attempts to order the film at temperatures above 650 K results in dissolution of Cr into the a-Fe2O3(0001) crystal based on SSIMS, an observation that is linked to the Fe3O4(111) termination of the surface and not to the properties of a-Cr2O3/a-Fe2O3 corundum interfaces. Nevertheless, this study shows that O2 plasma activation of Cr(CO)6 is an effect means of depositing Cr oxide films on surface without accompanying carbon contamination.