Oxygen Adlayer Research Articles

Resolving atomic diffusion in Ru(0001)−O(2×2) with spiral high-speed scanning tunneling microscopy

An intermediate state in atomic diffusion processes in the $\mathrm{O}(2\ifmmode\times\else\texttimes\fi{}2)$ layer on Ru(0001) is resolved with spiral high-speed scanning tunneling microscopy (STM). The diffusion of atomic oxygen in the adlayer has been studied by density functional theory and STM. Transition state theory proposes a migration pathway for the diffusion in the oxygen adlayer. With spiral scan geometries---a new approach to high-speed STM---the oxygen vacancy mobility on the highly covered Ru(0001) surface is determined to be in the range of 0.1 to 1 Hz. Experimental evidence for the intermediate state along the oxygen diffusion pathway is provided in real space and real time.

Guiding the design of oxidation-resistant Fe-based single atom alloy catalysts with insights from configurational space.

The high activity and selectivity of Fe-based heterogeneous catalysts toward a variety of reactions that require the breaking of strong bonds are offset in large part by their considerable instability with respect to oxidative deactivation. While it has been shown that the stability of Fe catalysts is considerably enhanced by alloying them with precious metals (even at the single-atom limit), rational design criteria for choosing such secondary metals are still missing. Since oxidative deactivation occurs due to the strong binding of oxygen to Fe and reduction by adsorbed hydrogen mitigates the deactivation, we propose here to use the binding affinity of oxygen and hydrogen adatoms as the basis for rational design. As it would also be beneficial to use cheaper secondary metals, we have scanned over a large subset of 3d-5d mid-to-late transition metal single atoms and computationally determined their effect on the oxygen and hydrogen adlayer binding as a function of chemical potential and adsorbate coverage. We further determine the underlying chemical origins that are responsible for these effects and connect them to experimentally tunable quantities. Our results reveal a reliable periodic trend wherein oxygen binding is weakened greatest as one moves right and down the periodic table. Hydrogen binding shows the same trend only at high (but relevant) coverages and otherwise tends to have its binding slightly increased in all systems. Trends with secondary metal coverage are also uncovered and connected to experimentally tunable parameters.

Oxygen intercalation in PVD graphene grown on copper substrates: A decoupling approach

We investigate the intercalation process of oxygen in-between a PVD-grown graphene layer and different copper substrates as a methodology for reducing the substrate-layer interaction. This growth method leads to an extended defect-free graphene layer that strongly couples with the substrate. We have found, by means of X-ray photoelectron spectroscopy, that after oxygen exposure at different temperatures, ranging from 280 °C to 550 °C, oxygen intercalates at the interface of graphene grown on Cu foil at an optimal temperature of 500 °C. The low energy electron diffraction technique confirms the adsorption of an atomic oxygen adlayer on top of the Cu surface and below graphene after oxygen exposure at elevated temperature, but no oxidation of the substrate is induced. The emergence of the 2D Raman peak, quenched by the large interaction with the substrate, reveals that the intercalation process induces a structural undoing. As suggested by atomic force microscopy, the oxygen intercalation does not change significantly the surface morphology. Moreover, theoretical simulations provide further insights into the electronic and structural undoing process. This protocol opens the door to an efficient methodology to weaken the graphene-substrate interaction for a more efficient transfer to arbitrary surfaces.

Oxygen Adsorption and Water Formation on Co(0001)

Oxygen adsorption and removal on flat and defective Co(0001) surfaces have been investigated experimentally using scanning tunneling microscopy, temperature-programmed and isothermal reduction, synchrotron X-ray photoemission spectroscopy, and work function measurements under ultrahigh vacuum conditions and H2/CO pressures in the 10–5 mbar regime. Exposure of the Co(0001) to O2(g) at 250 K leads to the formation of p(2 × 2) islands with a local coverage of 0.25 ML. Oxygen adsorption continues beyond 0.25 ML, reaching a saturation point of ∼0.39 ML Oad, without forming cobalt oxide. Chemisorbed oxygen adlayers can be reduced on both flat and defective Co(0001) surfaces by heating in the presence of ∼2.3 × 10–5 mbar H2(g). The onset of the oxygen removal as water during temperature-programmed reduction experiments (1 K s–1) is at around 450 K on flat Co(0001) and 550 K on defective Co(0001). By evaluation of isothermal reduction experiments using a kinetic model, the activation energy for water formation is...

Dissociative adsorption of O2on unreconstructed metal (100) surfaces: Pathways, energetics, and sticking kinetics

An accurate description of oxygen dissociation pathways and kinetics for various local adlayer environments is key for an understanding not just of the coverage dependence of oxygen sticking, but also of reactive steady states in oxidation reactions. Density functional theory analysis for M(100) surfaces with $M=\text{Pd}$, Rh, and Ni, where O prefers the fourfold hollow adsorption site, does not support the traditional Brundle-Behm-Barker picture of dissociative adsorption onto second-nearest-neighbor hollow sites with an additional blocking constraint. Rather adsorption via neighboring vicinal bridge sites dominates, although other pathways can be active. The same conclusion also applies for $M=\text{Pt}$ and Ir, where oxygen prefers the bridge adsorption site. Statistical mechanical analysis is performed based on kinetic Monte Carlo simulation of a multisite lattice-gas model consistent with our revised picture of adsorption. This analysis determines the coverage and temperature dependence of sticking for a realistic treatment of the oxygen adlayer structure.

Locating Catalytically Active Oxygen on Ag(1 1 1)—A Spectromicroscopy Study

AbstractThe loading of an Ag(1 1 1) sample with oxygen was monitored by in situ low‐energy electron microscopy and X‐ray photoemission electron microscopy during NO2 dosing at T≥480 K. At first, adsorbed oxygen populates the Ag(1 1 1) surface, which initiates the (4×4) reconstruction leading to the characteristic O 1s core level at 528.30 eV. The formation of this phase proceeds on a mesoscopic length scale by traveling fronts separating reconstructed from non‐reconstructed surface areas. Continued NO2 dosing leads to the accumulation of a new oxygen species mainly at steps and step bunches. Characterized by an O 1s peak with two components at 530.20 eV and 530.75 eV, this species represents the active oxygen during the ethylene epoxidation reaction over Ag. The 530.20 eV component is attributed to surface oxygen, the 530.75 eV species to subsurface oxygen. This inhomogeneous accumulation of the active oxygen occurs at a very low rate. However, the preparation route can be changed, which strongly accelerates the population of the catalytically active oxygen species and leads to a homogeneous distribution of oxygen on the surface. This route involves the complete formation of the O(4×4) reconstruction by NO2 dosing, followed by a complete de‐reconstruction of the surface by desorption of the oxygen adlayer. The faster population kinetics is related to the Ag adatom transport during such a reconstruction/de‐reconstruction cycle.

Local structural models of complex oxygen- and hydroxyl-rich GaP/InP(001) surfaces

We perform density-functional theory calculations on model surfaces to investigate the interplay between the morphology, electronic structure, and chemistry of oxygen- and hydroxyl-rich surfaces of InP(001) and GaP(001). Four dominant local oxygen topologies are identified based on the coordination environment: M-O-M and M-O-P bridges for the oxygen-decorated surface; and M-[OH]-M bridges and atop M-OH structures for the hydroxyl-decorated surface (M = In, Ga). Unique signatures in the electronic structure are linked to each of the bond topologies, defining a map to structural models that can be used to aid the interpretation of experimental probes of native oxide morphology. The M-O-M bridge can create a trap for hole carriers upon imposition of strain or chemical modification of the bonding environment of the M atoms, which may contribute to the observed photocorrosion of GaP/InP-based electrodes in photoelectrochemical cells. Our results suggest that a simplified model incorporating the dominant local bond topologies within an oxygen adlayer should reproduce the essential chemistry of complex oxygen-rich InP(001) or GaP(001) surfaces, representing a significant advantage from a modeling standpoint.

How Surface Reactivity Depends on the Configuration of Coadsorbed Reactants: CO Oxidation on Rh(100)

LEED. TPRS. and RAIRS experiments combined with DFT calculations have been used to study CO oxidation on Rh(100) from preadsorbed O and CO and to unravel how the reaction kinetics is influenced by the configuration of the adsorbed reactants. At least four different regimes are identified in increasing order of reactivity: near zero coverage, isolated CO and O species react with the highest activation energy observed in this work (105 ± 4 kJ/mol). In the second regime. oxygen is present in a p(2 x 2) structure and reacts with bridge bonded CO, with an activation energy of 77 ± 8 kJ/mol. In the third regime. the reactivity is associated with on-top CO in defects of a c(2 x 2) oxygen layer. at an estimated activation energy of 58 ± 10 kJ/mol. In the last and most reactive regime. the oxygen adlayer has (2 x 2)-pg order with the top metal layer reconstructed. According to DFT calculations. CO adsorption lifts the reconstruction. Oxygen occupies 4-fold hollow and bridge sites: the latter react with bridged CO. The general trend is that if the reactants become destabilized by repulsive lateral interactions. the rate of reaction to CO 2 increases.

Mechanism and site requirements for NO oxidation on Pd catalysts

Abstract Kinetic and isotopic methods were used to establish the identity and kinetic relevance of elementary steps and the effects of cluster size for NO oxidation on supported Pd catalysts. O 2 activation on vacancies within nearly saturated oxygen adlayers is the sole kinetically relevant step. Water, present in combustion effluents, inhibits NO oxidation via reversible adsorption on vacancies to form unreactive OH species. The coverage and chemical potential of oxygen are determined by the NO 2 /NO ratios prevalent during catalysis; they are rigorously described by O 2 virtual pressures accessible to measurement. At a given oxygen chemical potential, O 2 activation during 16 O 2 – 18 O 2 exchange and NO oxidation occurs at similar rates, indicating that NO-assisted O 2 activation is not required for NO oxidation turnovers. These findings confirm the rigor and relevance of O 2 virtual pressure as a measurable surrogate for the oxygen chemical potential during catalysis, as well as the role of mobile oxygen species, which allow O 2 dissociation to occur on isolated vacancies. Oxygen chemical potentials prevalent during NO oxidation cause active clusters to exist as PdO at all relevant conditions, consistent with steady-state turnover rates that are insensitive to reductive or oxidative treatments. NO oxidation turnover rates decrease as PdO clusters become smaller because of stronger oxygen binding and lower vacancy concentrations in small clusters. The catalytic consequences of size are similar on PdO and Pt clusters, despite their different oxidation state, consistent with a common requirement for surface vacancies in O 2 activation steps on both catalysts. Such requirements lead to strong NO 2 inhibition effects and to a marked increase in NO oxidation rates when NO 2 adsorbents, present as physical mixtures, decrease NO 2 concentrations near active sites.

Structural imaging of surface oxidation and oxidation catalysis on Ru(0001)

Using simultaneous imaging and structural fingerprinting under reaction conditions, we probe the initial oxidation pathway and CO oxidation catalysis on Ru(0001). Oxidation beyond an initial $(1\ifmmode\times\else\texttimes\fi{}1)\text{-O}$ adlayer phase produces a heterogeneous surface, comprising a disordered trilayerlike surface oxide and an ordered ${\text{RuO}}_{2}(110)$ thin-film oxide, which form independently and exhibit similar stability. The surface oxide and ${\text{RuO}}_{2}$ phases both show high intrinsic catalytic activity. The oxygen adlayer is inactive in isolation but becomes active due to cooperative effects in close proximity to the surface oxide.

Ab initio study of element segregation and oxygen adsorption on PtPd and CoCr binary alloy surfaces

The segregation behavior of the bimetallic alloys PtPd and CoCr in the case of bare surfaces and in the presence of an oxygen ad-layer has been studied by means of first-principles modeling based on density-functional theory (DFT). For both systems, change of the d-band filling due to charge transfer between the alloy components, resulting in a shift of the d-band center of surface atoms compared to the pure components, drives the surface segregation and governs the chemical reactivity of the bimetals. In contrast to previous findings but consistent with analogous PtNi alloy systems, enrichment of Pt atoms in the surface layer and of Pd atoms in the first subsurface layer has been found in Pt-rich PtPd alloy models, despite the lower surface energy of pure Pd compared to pure Pt. Similarly, Co surface and Cr subsurface segregation occurs in Co-rich CoCr alloys. However, in the presence of adsorbed oxygen, Pd and Cr occupy preferentially surface sites due to their lower electronegativity and thus stronger oxygen affinity compared to Pt and Co, respectively. In either cases, the calculated oxygen adsorption energies on the alloy surfaces are larger than on the pure components when the more noble components are present in the subsurface layers.

A reactive oxygen state at a barium promoted Au (100) surface: the oxidation of ethene at cryogenic temperatures

Although Au (100) does not adsorb oxygen at either 295 K or 80 K, a barium modified Au(100) surface is active in oxygen dissociation resulting, through surface diffusion of oxygen adatoms, in the formation of a chemisorbed oxygen adlayer. This oxygen species is inactive for ethene oxidation, as is the oxygen species pre-adsorbed at an Au(100)-Ba surface at 80 K, and the clean Au(100)-Ba surface. However, when molecularly adsorbed ethene present at a Au(100)-Ba surface at 80 K is exposed to dioxygen and warmed to 140 K, surface carbonate is observed. We conclude that a transient oxygen species is the oxidant.

Reactivity and Structural Aspects of Cesium and Oxygen States at Cu(110) Surfaces: An XPS and STM Investigation

Structural and reactivity aspects of Cu(110)−Cs and Cu(110)−Cs/O overlayers have been investigated by XPS and STM. The development of cesium-induced structures at a Cu(110)−Cs overlayer has been followed as a function of cesium coverage at 295 K and the reactivity of the overlayer first to oxygen and subsequently to ammonia and carbon dioxide studied. For cesium concentrations up to 1.3 × 1014 cm-2 an incommensurate pseudo square structure is observed which is in registry with the copper substrate in the 〈100〉 direction. This coexists, at 1.3 × 1014 Cs adatoms cm-2, with a structure consisting of 〈11̄0〉-orientated rows which are not atomically resolved but have a spacing in the 〈100〉 direction of 1.1 nm. At a cesium concentration of 1.5 × 1014 cm-2, patches of structure with an inter-row spacing of 0.7 nm are present, and at a cesium concentration of 1.9 × 1014 cm-2, only the latter spacing is observed. An increase in cesium concentration to 2.1 × 1014 cm-2 results in an increase in the inter-row spacing to 1.1 nm. Exposure of cesium-modified surfaces to oxygen results in the development of new terraces superimposed upon the cesium-modified surface with the latter structurally unchanged by the formation of the oxygen adlayer, although there is a change in the XP binding energy of the Cs(3d) peaks. The new terraces consist of 〈100〉-orientated chains similar to those observed at unmodified Cu(110) surfaces; however, at low cesium concentrations these chains are arranged in (3 × 1) as well as (2 × 1) domains and at high cesium concentrations a c(6 × 2)O structure develops with an exposure of oxygen as low as 10 L. The adsorption of cesium at partially preoxidized surfaces results in the formation of a c(2 × 4) structure and also structures which have no simple relationship with the substrate lattice and which we assign to strained Cu−O (2 × 1) structures. At a surface with a complete monolayer of oxygen present the cesium forms 〈11̄0〉 chains with a minimum interchain spacing of 0.5 nm and alternate chains showing well-resolved maxima with a spacing of 0.5 nm. The adatoms in between the chains are less well-defined suggesting a degree of mobility in the 〈11̄0〉 direction. In comparison with oxygen at unmodified Cu(110) surfaces, oxygen states at the cesium-modified surface are unreactive to ammonia at 295 K, reaction only occurring after exposures of 300 L at 490 K. However, the cesium surface is reactive to carbon dioxide chemisorption at 295 K resulting in a surface carbonate with extensive migration of cesium and the emergence of areas of the underlying copper surface.

Lattice-gas modeling of the formation and ordering of oxygen adlayers on Pd(100)

Abstract We construct a lattice-gas (LG) model to describe not just the ordering of equilibrated adlayers of chemisorbed oxygen on Pd(1 0 0), but also the non-equilibrium ordering observed during dissociative adsorption of molecular oxygen on Pd(1 0 0). First, by combining transfer matrix analysis and Monte Carlo simulations, we determine the equilibrium phase diagrams for candidate LG models with pairwise-additive interactions including nearest-neighbor (NN) exclusion, second NN repulsion, third NN attraction, and possibly fourth NN repulsion. These interactions are selected so as to recover the p(2×2) and c(2×2) ordering observed in experiment. Interaction strengths are assessed by matching simulated and experimental phase diagrams. Second, a kinetic model is constructed to describe dissociative adsorption of molecular oxygen on second NN empty sites (consistent with NN exclusion), as well as subsequent thermally activated surface diffusion, and adlayer formation. Hopping rates for the latter reflect the selected adspecies interactions through detailed-balance constraints. By comparing simulated diffracted intensities for non-equilibrium adlayer structure during adsorption with experimental data for various temperatures and pressures, we demonstrate the existence of transient mobility for dissociative adsorption in this system, and also determine the magnitude of the thermal diffusion barrier.

Oxygen species in Cs/O activated gallium nitride (GaN) negative electron affinity photocathodes

Negative electron affinity (NEA) photocathode electron sources operating within sealed off tubes (closed vacuum) and demountable vacuum systems (open vacuum), suffer from different factors that affect the initial high performance and longevity. To aid in the understanding of the factors affecting an open vacuum system, the chemistry of a cesium and oxygen (Cs/O) adlayer was investigated, focusing on the role of oxygen during the NEA co-deposition process (activation) and operation of a GaN (0001) emitter. Synchrotron radiation photoemission spectroscopy and a focused mercury arc discharge lamp are used for analyzing surface chemical species and total quantum yield, respectively, as the photocathode ages. The results for the activation within a demountable vacuum system indicated: (1) oxygen concentration increased over time on the Cs/O activated surface independent of the starting substrate as observed in related studies of InP (100) and GaAs (100), (2) the dominant initial oxygen species is assigned to an ion of molecular oxygen (di-oxygen) in the Cs/O activation layer having −2 charge state that changes to the −1 charge state as the quantum yield decays, and (3) the chemical changes of the Cs/O adlayer are not accompanied by a significant loss of cesium from the surface, but instead an increase in oxygen from the open vacuum system occurred. We present a chemical model for the activation layers and their transformation over time consistent with observations (1) through (3). The quantum efficiency (QE) from the GaN (0001) photocathode remained constant within a few percent over a 10 h period at ⩾20% QE and decayed by less than a factor of 2 over the subsequent 7 h as the chemical changes at the surface took place. The slowly decreasing monotonic yield gives preliminary evidence that GaN is a prospect for a more robust emitter. A long lived photocathode of this type offers near constant quantum yield over several hours when operating within open vacuum conditions by simply adjusting laser power with a feedback circuit. On the other hand, this decay can most certainly be avoided in sealed tubes by maintaining a pristine closed off environment with the proper over pressure of Cs. A detailed account of the effects of the chemical changes in the Cs/O adlayer on the resulting emission properties for GaAs and GaN (open vacuum) are discussed in a separate report [F. Machuca et al., J. Vac. Sci. Technol. B 20, 2721 (2002)].

Spontaneous and electron-induced adsorption of oxygen on Au([formula omitted])-(1×2)

The interaction of dioxygen with a gold(110)-(1×2) surface has been investigated between 28 and 700 K by means of thermal desorption spectroscopy (TDS), UV photoelectron spectroscopy (UPS), work function measurements (ΔΦ), low-energy electron diffraction (LEED), and near-edge X-ray absorption spectroscopy (NEXAFS). It proves that Au––unlike most of the other metals including its congeners Cu and Ag––does not spontaneously dissociate physisorbed molecular oxygen. Rather, additional activation of the physisorbed O2 either by electron or by photon impact is required to make the oxygen chemisorb. Below 50 K, dioxygen adsorbs readily with a binding energy <12 kJ/mol, causing a work function decrease of ΔΦ=0.22 eV at Θ=1.0 ML. TDS reveals three molecular desorption states with first-order kinetics around 51 and 45 K (first layer), and at 37 K (second layer). A zeroth-order peak around 34 K corresponds to multilayer desorption. Both UPS and NEXAFS exhibit signals typical for physisorbed O2. Irradiation of physisorbed O2 layers with low-energy electrons or UV photons produces chemisorbed oxygen, providing a convenient possibility for the preparation of chemisorbed oxygen adlayers. The chemisorbed oxygen species is characterized by a single desorption state above 500 K, with second-order kinetics at low coverages (Θ<0.25 ML) suggesting adsorbed oxygen atoms. A desorption energy of 140±3 kJ/mol was determined. Another desorption peak around 490 K and at coverages >1.0 ML is associated with the decomposition of an oxidic species. LEED observations reveal that chemisorbed oxygen destroys the long-range order of the Au substrate surface. Our results provide possible explanations for the `beam damage' often observed in UPS/LEED experiments with adsorbed dioxygen.

Reactions of gas-phase H atoms with atomically and molecularly adsorbed oxygen on Pt(111)

The interaction of gas-phase H atoms with ordered and disordered adlayers of atomic oxygen, hydroxyl, and molecular oxygen on Pt(111) surfaces was investigated by in situ mass spectrometry and post-reaction TPD (temperature programed desorption). Exposure of oxygen adlayers to gas-phase H atoms at 85 K leads to formation of H2O via two consecutive hydrogenation reactions: H(g)+O(a)→OH(a) followed by H(g)+OH(a)→H2O(g,a). Both reaction steps are highly exothermic, and nascent H2O molecules partially escape into the gas phase before being thermally accommodated on the surface. Empty surface sites and hydrogen bonding promote thermalization of H2O. Separate experiments performed with OH-covered Pt(111) surfaces reveal that the hydrogenation of hydroxyl is a slow reaction compared to the hydrogenation of atomic oxygen; additionally, the abstraction of H from OH by gas-phase D atoms, OH(a)+D(g)→O(a)+HD(g), was detected. Abstraction of H from adsorbed H2O was not observed. Admission of gas-phase H atoms to O2-covered Pt(111) surfaces at 85 K leads to the desorption of O2 and H2O. The thermodynamic stability of the HO2 radical suggests that the reaction is initiated by hydrogenation of molecular oxygen, O2(a)+H(g)→HO2. The intermediate HO2 either decomposes via dissociation of the HO–O bond, HO2→OH(a)+O(a), finally leading to the formation of H2O (∼85%), or via dissociation of the H–O2 bond thus leading to desorption of O2 (∼15%). The whole reaction sequence of formation and decomposition of HO2 is fast compared to the formation of H2O via hydrogenation of atomic oxygen and hydroxyl. The observed coverage dependence of the reaction kinetics indicates the dominance of hot-atom mediated reactions.

In Situ Scanning Tunneling Microscopy of (Bi)sulfate, Oxygen, and Iodine Adlayers Chemisorbed on a Well-Defined Ru(001) Electrode Prepared in a Non-Ultrahigh-Vacuum Environment

This work shows that it is possible to prepare a well-defined Ru(001) surface by annealing in an airtight quartz cell purged continuously with hydrogen gas. Cyclic voltammograms obtained in 0.1 M hydrofluoric and perchloric acid solutions contain clear redox characteristics, owing to the interfacial events of hydrogen adsorption/desorption and formation/reduction of an oxygen adlayer. High-quality in situ scanning tunneling microscopy (STM) atomic imaging reveals the hexagonal lattice of the Ru(001) substrate in perchloric acid solutions at the onset of hydrogen evolution. Irreversible adsorption of the (bi)sulfate anions from 0.1 M sulfuric acid at −0.1 V (vs Ag/AgCl) renders a highly ordered structure, identified as (√3 × √7)oblique by in situ STM. This arrangement of (bi)sulfate anions is the same as those found at the (111) surfaces of Au, Pt, Rh, Pd, Ir, and Cu electrodes. Potential excursion to 0.4 V results in a well-ordered (2 × 2) oxygen adlayer at the expense of the (√3 × √7)oblique (bi)sulfate ...

An investigation of the surface reactivity of diamond photocathodes with molecular and atomic oxygen species

The surface reactivity of CVD diamond films, which function as UV photocathodes, with thermal and electronically excited O 2, as well as atomic oxygen, has been explored. The CVD films show a low, but measurable reactivity with O 2, which increases markedly with electronic excitation, to form dilute oxygen adlayers which are stable thermally to 800 K. In contrast, reaction with atomic O produces significantly higher surface concentrations of oxygen, although these adlayers decompose thermally below 500 K, evolving CO 2. Greater surface reaction probabilities are observed if the diamond surface is pre-hydrogenated before interaction with oxygen. The consequences of these observations for the stable operation of H-terminated diamond photocathodes are discussed.

Site switching and restructuring of oxygen adlayers induced by high coverage NO on Co{101̄0} at 100 K

We have employed reflection–absorption IR spectroscopy (RAIRS) as the principal technique as well as low energy electron diffraction (LEED) and temperature programmed desorption (TPD) as diagnostic tools to study the adsorption and reaction of nitric oxide (NO) on oxygen precovered Co{101̄0} surfaces at 100 K. The presence of oxygen adatoms greatly attenuates the occupation of two-fold sites in favor of atop sites, but O adatoms do not show any significant blocking effect for NO adsorption, and the NO coverage is close to 0.5 ML, as found on the clean surface. Beyond a critical coverage of NO, whatever the initial O coverage, a new IR band appears at ∼1876 cm−1 which is indicative of a strong NO–O interaction. The coadsorption of NO with various precoverages of oxygen (0.15–1.0 ML) including three ordered oxygen overlayers, c(2×4) (θO≈0.5 ML), p(2×1) (θO≈0.5 ML), and p(2×1)-g (θO≈1.0 ML), reveals an NO-induced surface restructuring process, in which O adatoms are driven from overlayer to underlayer sites at high NO coverages. This restructuring process increases the O effective diameter to up to ∼10 Å, this being the range over which the NO–O interaction is strong, producing the 1870 cm−1 N–O band.