Characterization of atomic step structures on CaF<sub>2</sub>(111) by their electric potential

Pieper, H. H.; Barth, Clemens; Reichling, Michael

doi:10.1063/1.4739944

Cited by 19 publications

(12 citation statements)

References 30 publications

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“…The reason for this remains unknown so far. The bright contrast at the edges of the ceria NPs can be assigned to a more negative potential at the edges, probably produced by low coordinated negative atomic species like unscreened O ions as observed before on thick ceria films [67] and similar ionic surfaces like CaF 2 (111) [68].…”

Section: Oxidationsupporting

confidence: 56%

High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

Barraj¹,

Chatelain²,

Barth³

2021

J. Phys.: Condens. Matter

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The inverse catalyst 'cerium oxide (ceria) on copper' has attracted much interest in recent time because of its promising catalytic activity in the water-gas-shift reaction and the hydrogenation of CO 2 . For such reactions it is important to study the redox behaviour of this system, in particular with respect to the reduction by H 2 . Here, we investigate the high-temperature O 2 oxidation and H 2 reduction of ceria nanoparticles (NP) and a Cu(111) support by low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). After oxidation at 550 °C, the ceria NPs and the Cu(111) support are fully oxidized, with the copper oxide exhibiting a new oxide structure as verified by LEED and STM. We show that a high H 2 dosage in the kilo Langmuir range is needed to entirely reduce the copper support at 550 °C. A work function (WF) difference of φ rCeria/Cu-Cu ≈ -0.6 eV between the ceria NPs and the metallic Cu(111) support is measured, with the Cu(111) surface showing no signatures of separated and confined surface regions composed by a CuCe alloy. After oxidation, the WF difference is close to zero ( φ Ceria/Cu-Cu ≈ -0.1 . . . 0 eV), which probably is due to a WF change of both, ceria and copper.

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Section: Oxidationsupporting

confidence: 56%

High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

Barraj¹,

Chatelain²,

Barth³

2021

J. Phys.: Condens. Matter

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“…39 A positive charge is represented by a bright shading while a negative charge is coded dark. 40 X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) experiments are also performed at room temperature in separate vacuum systems after transfer of the sample through the ambient atmosphere. XPS spectra are recorded using a PHI 5600ci multitechnique spectrometer (Physical Electronics, Chanhassen, MN, USA) with monochromatic Al K a radiation (hn = 1486.6 eV) of 0.3 eV FWHM bandwidth.…”

Section: Experimental Methodsmentioning

confidence: 99%

Morphology and nanostructure of CeO2(111) surfaces of single crystals and Si(111) supported ceria films

Pieper

Derks

Zoellner

et al. 2012

Phys. Chem. Chem. Phys.

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The surface morphology of CeO(2)(111) single crystals and silicon supported ceria films is investigated by non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) for various annealing conditions. Annealing bulk samples at 1100 K results in small terraces with rounded ledges and steps with predominantly one O-Ce-O triple layer height while annealing at 1200 K produces well-ordered straight step edges in a hexagonal motif and step bunching. The morphology and topographic details of films are similar, however, films are destroyed upon heating them above 1100 K. KPFM images exhibit uniform terraces on a single crystal surface when the crystal is slowly cooled down, whereas rapid cooling results in a significant inhomogeneity of the surface potential. For films exhibiting large terraces, significant inhomogeneity in the KPFM signal is found even for best possible preparation conditions. Applying X-ray photoelectron spectroscopy (XPS), we find a significant contamination of the bulk ceria sample with fluorine while a possible fluorine contamination of the ceria film is below the XPS detection threshold. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) reveals an accumulation of fluorine within the first 5 nm below the surface of the bulk sample and a small concentration throughout the crystal.

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“…132 As ceria crystallises in the fluorite structure, two different types of step edges, namely type-A and type-B, are relevant for a growth process on the (111) surface. 23,133 The probability for particle attachment is higher at steps of type-A so that type-B steps grow faster and preferentially triangles are grown, although, the substrate exhibits a hexagonal surface symmetry. 130 The pyramidal structures are commonly referred to as wedding cakes that are the result of a multilayer growth in the presence of a significant Ehrlich-Schwoebel barrier.…”

Section: Iii2 Surface Structure and Morphologymentioning

confidence: 99%

Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems

Niu

Zoellner

Schroeder

et al. 2015

Phys. Chem. Chem. Phys.

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Rare earth praseodymium and cerium oxides have attracted intense research interest in the last few decades, due to their intriguing chemical and physical characteristics. An understanding of the correlation between structure and properties, in particular the surface chemistry, is urgently required for their application in microelectronics, catalysis, optics and other fields. Such an understanding is, however, hampered by the complexity of rare earth oxide materials and experimental methods for their characterisation. Here, we report recent progress in studying high-quality, single crystalline, praseodymium and cerium oxide films as well as ternary alloys grown on Si(111) substrates. Using these well-defined systems and based on a systematic multi-technique surface science approach, the corresponding physical and chemical properties, such as the surface structure, the surface morphology, the bulk-surface interaction and the oxygen storage/release capability, are explored in detail. We show that specifically the crystalline structure and the oxygen stoichiometry of the oxide thin films can be well controlled by the film preparation method. This work leads to a comprehensive understanding of the properties of rare earth oxides and highlights the applications of these versatile materials. Furthermore, methanol adsorption studies are performed on binary and ternary rare earth oxide thin films, demonstrating the feasibility of employing such systems for model catalytic studies. Specifically for ceria systems, we find considerable stability against normal environmental conditions so that they can be considered as a "materials bridge" between surface science models and real catalysts.

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Characterization of atomic step structures on CaF₂(111) by their electric potential

Cited by 19 publications

References 30 publications

High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

Morphology and nanostructure of CeO2(111) surfaces of single crystals and Si(111) supported ceria films

Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems

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Characterization of atomic step structures on CaF2(111) by their electric potential

Cited by 19 publications

References 30 publications

High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

High-temperature oxidation and reduction of the inverse ceria/Cu(111) catalyst characterized by LEED, STM, nc-AFM and KPFM

Morphology and nanostructure of CeO2(111) surfaces of single crystals and Si(111) supported ceria films

Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems

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Characterization of atomic step structures on CaF₂(111) by their electric potential