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Derouin, Jonathan; Farber, Rachael G.; Turano, Marie E.; Iski, Erin V.; and Killelea, Daniel. Thermally Selective Formation of Subsurface Oxygen in Ag(111) Just Accepted "Just Accepted" manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides "Just Accepted" as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. "Just Accepted" manuscripts appear in full in PDF format accompanied by an HTML abstract. "Just Accepted" manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). "Just Accepted" is an optional service offered to authors. Therefore, the "Just Accepted" Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the "Just Accepted" Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these "Just Accepted" manuscripts. Thermally Selective Formation of Subsurface Oxygen inAg (111) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 AbstractA long-standing challenge in the study of heterogeneously catalyzed reactions on silver surfaces has been the determination of what oxygen species are of greatest chemical importance.This is due to the coexistence of several different surface phases on oxidized silver surfaces. A further complication is subsurface oxygen (O sub ). O sub are O atoms absorbed into the near surface of a metal, and are expected to alter the surface in terms of chemistry and structure, but these effects have yet to be well characterized. We studied oxidized Ag(111) surfaces after exposure to gas-phase O atoms to determine how O sub is formed and how its presence alters the resultant surface structure. Using a combination of surface science techniques to quantify O sub formation and the resultant surface structure, we observed that once 0.1 ML of O sub has formed, the surface dramatically, and uniformly, reconstructed to a striped phase at the expense of all other surface phases. Furthermore, O sub formation was hindered at temperatures above 500 K.The thermal dependence for O sub formation suggests that at industrial catalytic conditions of 475 -500 K for the epoxidation of ethylene-to-ethylene oxide, O sub would be present and is a factor in the subsequent reactivit...

Oxygen chemisorption on rhodium surfaces gives rise to several surface structures depending on the total oxygen coverage. In this study, Rh(111) was exposed to O2 or O + O2, and the oxygen surface structures formed at coverages greater than or equal to 0.5 ML were imaged using scanning tunneling microscopy (STM). The STM images showed that the (2 × 1)-O adlayer domains are predominant on the Rh(111) surface. Exposure of Rh(111) to O atoms yielded O coverages greater than 0.5 ML; (1 × 1)-O domains were observed to form along terrace step edges, and their areal density increased with exposure. However, (2 × 1)-O adlayers were still present on the surface. The STM images reveal that the surface coverage was appreciably less than the total amount of oxygen, suggesting that O uptake resulted in significant absorption into the selvedge, even at modest surface O coverages and temperatures. We compare these observations to previous surface scattering experiments and calculations and demonstrate that our findings resolve several inconsistencies and clearly demonstrate that despite the apparent simplicity of the O/Rh system subtle details remain important, and multiple O structures were present at any O coverage from 0.25 to >1.0 ML. This indicates the rich complexity of O-transition metal interactions and suggests that accurate models of oxygen on rhodium surfaces must include several coexisting surface structures.

ThLf sec1ionLf imendedfor 1he fJuhlication of ( I ) An electrochemical method using pulsed alternating current etching (PACE) to produce atomically sharp scanning tunneling microscopy (STM) tips is presented. An Arduino Uno microcontroller was used to control the number and duration of the alternating current (AC) pulses, allowing for ready optimization of the procedures for both Pt:lr and W tips using a single apparatus. W tips prepared using constant and pulsed AC power were compared. Tips fashioned using PACE were sharper than those etched with continuous AC power alone. Pt:lr tips were prepared with an initial coarse etching stage using continuous AC power followed by fine etching using PACE. The number and potential of the finishing AC pulses was varied and scanning electron microscope imaging was used to compare the results. Finally, tip quality using the optimized procedures was verified by UHY-STM imaging. With PACE, at least 70% of the W tips and 80% of the Pt:lr tips were of sufficiently high quality to obtain atomically resolved images of HOPG or Ni(l 11 ).