Image of the Month

October 2017

The Quest for Stability: Structural Dependence of Rh(111) on Oxygen Coverage at Elevated Temperature

Figure 3. STM images after exposing Rh(111) to AO: (A) θO,total = 6.4 ML at Tdep = 700 K; (B) θO,total = 2.9 ML at Tdep = 350 K followed by 600 s anneal at 700 K; (C) θO,total = 0.9 ML at Tdep = 350 K followed by 600 s anneal at 700 K. Insets are LEED patterns (62 eV) taken after deposition. STM images were obtained at 30 K and conditions were (L to R) (A) 100 mV, 137 pA; 181 mV, 170 pA; 140 mV, 153 pA; (B) 50 mV, 400 pA; 70 mV, 410 pA; 50 mV, 400 pA; (C) 20 mV, 200 pA; 20 mV, 150 pA; 20 mV, 150 pA.

Recent studies have shown the importance of oxide surfaces in heterogeneously catalyzed reactions. Because of the difficulties in reproducibly preparing oxidized metal surfaces, it is often unclear what species are thermodynamically stable and what factors effect the oxide formation process. In this work, we show that the thermodynamically stable phases on Rh(111) after exposure to atomic oxygen are the (2×1)- O adlayer and the trilayer surface oxide, RhO2. Formation of RhO2 was facilitated by surface defects and elevated concentrations of dissolved O atoms in the subsurface region. As the concentration of subsurface O atoms decreased, the coverage of RhO2 decreased so that only the (2×1)- O adlayer was present on the surface. The importance of subsurface oxygen species in RhO2 formation and stability indicates a complex relationship between surface structure and subsurface oxygen concentration.

The Journal of Physical Chemistry C 121.19 (2017): 10470-10475

Rachael G. Farber,† Marie E. Turano,† Eleanor C. N. Oskorep,† Noelle T. Wands,† Erin V. Iski,‡ and Daniel R. Killelea*,†

†Department of Chemistry & Biochemistry, Loyola University Chicago, 1068 West Sheridan Road, Chicago, Illinois 60660, United States

‡Department of Chemistry and Biochemistry, The University of Tulsa, 800 South Tucker Drive, Tulsa, Oklahoma 74104, United States

Closed Cycle Pan Freedom System