Oxygen plasma activation of Cr(CO) 6 on α-Fe 2O 3(0001)

Abstract

The chemistry of Cr(CO) 6 on the Fe 3O 4(111) surface termination of α-Fe 2O 3(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 O 2 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 Fe 3O 4(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 O 2 plasma source at 100 K 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 CO 2 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 O 2 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 was disordered at 600 K and likely O-terminated based on subsequent water TPD. Attempts to order the film at temperatures above 650 K resulted in dissolution of Cr into the α-Fe 2O 3(0001) crystal based on SSIMS, an observation linked to the Fe 3O 4(111) termination of the surface and not to the properties of α-Cr 2O 3/α-Fe 2O 3 corundum interface. Nevertheless, this study shows that O 2 plasma activation of Cr(CO) 6 is an effective means of depositing Cr oxide films on surfaces without accompanying carbon contamination.