Synchrotron Radiation Scanning Photoemission Microscopy: Instrumentation and Application in Surface Science

Кискинова, М.; Marsi, M.; Fabrizio, E. Di; Gentili, M.

doi:10.1142/s0218625x99000287

Cited by 62 publications

(25 citation statements)

References 68 publications

(58 reference statements)

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“…The imaging mode in SPEM maps the lateral distribution of elements by collecting photoelectrons with a selected energy while scanning the specimen with respect to the focused beam. 16,17 .…”

Section: Methodsmentioning

confidence: 99%

Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆

Ray

Middey

Jana

et al. 2011

EPL

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The unusual magnetoresistance (M R) behavior in Sr 2 FeMoO 6 , recently termed as spin-valve type MR (SVMR), presents several anomalies that are little understood so far. The difficulty in probing the origin of this phenomenon, arising from the magnetic property of only a small volume fraction of the ferromagnetic bulk, is circumvented in the present study by the use of ac susceptibility measurements that are sensitive to the slope rather than the magnitude of the magnetization. The present study unravels a spin-glass (SG) like surface layer around each soft ferromagnetic (FM) grain of Sr 2 FeMoO 6 . It is also observed that there is a very strong exchange coupling between the two, generating 'exchange bias' effect, which consequently creates the 'valve', responsible for the unusual M R effects.

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Section: Methodsmentioning

confidence: 99%

Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆

Ray

Middey

Jana

et al. 2011

EPL

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“…The SPEM uses a zone plate as photon focusing optic and a hemispherical electron energy analyzer with a 48 channel detector [18]. It can be operated in imaging as well as in microspot XPS mode.…”

Section: X-ray Photoelectron Spectroscopy (Xps) and Xps Microscopymentioning

confidence: 99%

On the CO-Oxidation over Oxygenated Ruthenium

Rosenthal¹,

Girgsdies

Timpe

et al. 2009

Zeitschrift Für Physikalische Chemie

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The oxidation of carbon monoxide over polycrystalline ruthenium dioxide (RuO 2 ) powder was studied in a packed-bed reactor and by bulk and surface analytical methods. Activity data were correlated with bulk phases in an in-situ X-ray diffraction (XRD) setup at atmospheric pressure. Ruthenium dioxide was pre-calcined in pure oxygen at 1073 K. At this stage RuO 2 is completely inactive in the oxidation of CO. After a long induction period in the feed at 503 K RuO 2 becomes active with 100% conversion, while in-situ XRD reveals no changes in the RuO 2 diffraction pattern. At this stage selective roughening of apical RuO 2 facets was observed by scanning electron microscopy (SEM). Seldom also single lateral facets are roughened. EDX indicated higher oxygen content in the following order: flat lateral facets > rough lateral facets > rough apical facets. Further, experiments in the packed bed reactor indicated oscillations in the CO 2 formation rate. At even higher temperatures in reducing feed (533-543 K) the sample reduces to ruthenium metal according to XRD. The reduced particles exhibiting lower ignition temperature are very rough with cracks and deep star-shaped holes. An Arrhenius plot of the CO 2 formation rate below the ignition temperature reveals the reduced samples to be significantly more active based on mass unit and shows lower apparent activation energy than the activated oxidized sample. Micro-spot X-ray photoelectron spectroscopy (XPS) and XPS microscopy experiments were carried out on a Ru(0001) single crystal exposed to oxygen at different temperature. Although low energy electron diffraction (LEED) images show a strong 1x1 pattern, the XPS data indicated a wide lateral inhomogeneity with different degree of oxygen dissolved in the subsurface layers. All these and the literature data are discussed in the context of different active states and transport issues, and the metastable nature of a phase mixture under conditions of high catalytic activity.

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“…In order to visualize the reaction dynamics we employ photoemission electron microscopy (PEEM) which images the local work function. Direct chemical information is provided by scanning photoelectron microscopy (SPEM) -a technique that utilizes synchrotron radiation (600 eV) to eject photoelectrons from element-specific core levels [14]. It has been demonstrated in our previous experiments that reaction fronts initiated under reaction conditions not only remove chemisorbed oxygen but also induce a redistribution of the alkali metal leading to the formation of large K O islands [15][16][17].…”

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confidence: 99%

Promoter-Induced Reactive Phase Separation in Surface Reactions

Decker

Marbach²,

Hinz³

et al. 2004

Phys. Rev. Lett.

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Promoters are adsorbed mobile species which do not directly participate in a catalytic surface reaction, but can influence its rate. Often, they are characterized by strong attractive interactions with one of the reactants. We show that these conditions lead to a Turing instability of the uniform state and to the formation of reaction-induced periodic concentration patterns. Experimentally such patterns are observed in catalytic water formation on a Rh(110) surface in the presence of coadsorbed potassium. DOI: 10.1103/PhysRevLett.92.198305 PACS numbers: 82.40.Np, 68.43.Jk, 82.40.-g, 82.65.+r Reactive condensed matter may exhibit nonequilibrium pattern formation resulting from an interplay between reactions, diffusion, and energetic interactions between the reacting particles. Adding a reaction to a phase-separating polymer mixture generates periodic stationary patterns whose wavelength is directly controlled by the reaction rate [1][2][3]. Phase-separating two-component Langmuir monolayers with chemical reactions show spontaneous formation of traveling wave patterns [4,5]. Catalytic surface reactions provide another important example of such systems. Energetic interactions between adsorbed atoms or molecules often lead to two-dimensionally ordered adsorbate phases and structural phase transitions [6]. The theoretical analysis has shown that, with the additional presence of reaction and diffusion, stationary and traveling nonequilibrium patterns based on reactive phase separation can develop in such adsorbate layers [7][8][9]. In this Letter, we provide evidence that reactive phase separation may occur in a broad class of catalytic surface reactions involving promoters and poisons. Such phase separation is demonstrated experimentally with the catalytic surface reaction O 2 H 2 on a potassium-covered Rh(110) surface. Theoretically, we show that already a general model of a binary annihilation reaction in presence of a promoter species leads to such phenomena. Using a realistic model of the reaction, the experimental results can even be quantitatively reproduced.Promoters and poisons are substances which, adsorbed on a catalytic metal surface, can dramatically increase or decrease the rate of a catalytic reaction by their mere presence [10]. Alkali metals are a well-known example of a promoter species finding use in a number of technologically important catalytic reactions [10,11]. The specific system considered here is the O 2 H 2 reaction on a potassium-covered Rh(110) surface. Both gases, O 2 and H 2 , adsorb dissociatively and the atomic adsorbates then recombine forming water which rapidly desorbs [12]. The alkali metal represents an additional species that modifies the local catalytic activity but is not consumed by the reaction. It is very mobile on the oxygen free surface and has a high affinity to one of the reactants, namely, oxygen, with which it forms a number of well-ordered twodimensional coadsorbate phases [13]. In order to visualize the reaction dynamics we employ photoemission electron microsco...

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Synchrotron Radiation Scanning Photoemission Microscopy: Instrumentation and Application in Surface Science

Cited by 62 publications

References 68 publications

Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆

Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆

On the CO-Oxidation over Oxygenated Ruthenium

Promoter-Induced Reactive Phase Separation in Surface Reactions

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Synchrotron Radiation Scanning Photoemission Microscopy: Instrumentation and Application in Surface Science

Cited by 62 publications

References 68 publications

Origin of the unconventional magnetoresistance in Sr 2 FeMoO 6

Origin of the unconventional magnetoresistance in Sr 2 FeMoO 6

On the CO-Oxidation over Oxygenated Ruthenium

Promoter-Induced Reactive Phase Separation in Surface Reactions

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Product

Resources

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Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆

Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆