Fig. 1: Oxidation and wetting of cobalt films deposited on Au(111).
From: Elucidating the active phases of CoOx films on Au(111) in the CO oxidation reaction
a From the bottom: Co2p spectra of 1 MLE Co0 (black curve); after room temperature exposure to 1 × 10−6 Torr O2 for 1 min (CoO0.25, red); after oxidation under 1 × 10−6 Torr O2 at 200 °C for 10 min (CoO, blue); and under 105 mTorr of O2-rich gas conditions (CO:O2 = 1:20) at 200°C (Co3O4, green). The dotted vertical lines mark the binding energy positions of the 2p3/2 core levels of metallic Co (Co0), CoO (Co2+), Co3O4 (Co2+ and Co3+), and their shake-up peak satellites (Cosat2+ and Cosat3+). b Corresponding O 1 s core level regions. From the bottom: mostly clean metallic Co (black); CoO0.25 film (red); and after 10 min exposure to 1 × 10−6 Torr O2 at 200 °C (blue). c Au4f core level spectral region. From bottom: clean Au (gray curve); after deposition of 1 MLE of Co (black curve); after annealing under 1 × 10−6 Torr O2 at 200 °C for 10 min (red); and after 10 min exposure to 1 × 10−6 Torr O2 at 200 °C (blue). The strong decrease of the Au 4 f peak intensity is due to the spreading of the CoOx film, now covering more Au surface than the initial metallic film. On the right is a schematic illustration of the wetting process during the oxidation process. The XPS data were acquired at beamline 23-ID-2 (IOS) of NSLS-II.
