Scanning Tunneling Microscope Study of Surface Morphology Variation of CeO<sub>2</sub>(111) with Changing Annealing Condition

Shahed, Syed Mohammad Fakruddin; Sainoo, Yasuyuki; Komeda, Tadahiro

doi:10.1143/jjap.50.08lb05

Cited by 8 publications

(10 citation statements)

References 35 publications

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“…Given the very low tunneling current of the measurements, it is possible that there are angular effects and/or non-negligible tip–surface interactions, which may be responsible for these features; in any case their origin remains unexplained. Furthermore, the pairing is not observed in all experiments (see Shahed et al, 2011 for example), which could be due to weaker tip–surface interactions.…”

Section: Resultsmentioning

confidence: 84%

STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

et al. 2019

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We present a theoretically oriented analysis of the appearance and properties of plausible candidates for the anionic defects observed in scanning tunneling microscopy (STM) experiments on CeO 2 (111). The simulations are based on density functional theory (DFT) and cover oxygen vacancies, fluorine impurities and hydroxyl groups in the surface and sub-surface layers. In the surface layer, all three appear as missing spots in the oxygen sublattice in filled state simulated STM images, but they are distinguishable in empty state images, where surface oxygen vacancies and hydroxyls appear as, respectively, diffuse and sharp bright features at oxygen sites, while fluorine defects appear as triangles of darkened Ce ions. In the sub-surface layer, all three defects present more complex patterns, with different combinations of brightened oxygen ion triangles and/or darkened Ce ion triangles, so we provide image maps to support experimental identification. We also discuss other properties that could be used to distinguish the defects, namely their diffusion rates and distributions.

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Section: Resultsmentioning

confidence: 84%

STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

et al. 2019

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“…preferential growth along the crystalographically equivalent step edges. 13 In Fig. 1(b), we show the STM image of the film deposited at the substrate temperature of 1060 K, which is only 20 K higher than that used for Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The substrates used in such researches include Pd(111), 4 Pt(111), [5][6][7] Rh(111), 8 Ni(111), 9 Cu(111), 10,11 and Ru(0001). 9,[12][13][14][15] It has been pointed out that step-edges, kinks, and vacancies are active sites for the catalytic reaction. 16,17 In order to examine the role of surface active sites, it is required to prepare the surface with wider terraces, straight steps, and low vacancy numbers.…”

Section: Introductionmentioning

confidence: 99%

Epitaxial growth of CeO2(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

Hasegawa¹,

Shahed²,

Sainoo³

et al. 2014

The Journal of Chemical Physics

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We formed an epitaxial film of CeO2(111) by sublimating Ce atoms on Ru(0001) surface kept at elevated temperature in an oxygen ambient. X-ray photoemission spectroscopy measurement revealed a decrease of Ce4+/Ce3+ ratio in a small temperature window of the growth temperature between 1070 and 1096 K, which corresponds to the reduction of the CeO2(111). Scanning tunneling microscope image showed that a film with a wide terrace and a sharp step edge was obtained when the film was grown at the temperatures close to the reduction temperature, and the terrace width observed on the sample grown at 1060 K was more than twice of that grown at 1040 K. On the surface grown above the reduction temperature, the surface with a wide terrace and a sharp step was confirmed, but small dots were also seen in the terrace part, which are considerably Ce atoms adsorbed at the oxygen vacancies on the reduced surface. This experiment demonstrated that it is required to use the substrate temperature close to the reduction temperature to obtain CeO2(111) with wide terrace width and sharp step edges.

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“…41 Recent investigations revealed a strong dependence of the morphology on the annealing time. 42 In these experiments, the time to reach the desired temperature has been chosen to be as short as 40 s. 43 We have tried several preparation procedures, and developed a standard procedure involving much slower heating.…”

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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Scanning Tunneling Microscope Study of Surface Morphology Variation of CeO₂(111) with Changing Annealing Condition

Cited by 8 publications

References 35 publications

STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

Epitaxial growth of CeO2(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

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

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Scanning Tunneling Microscope Study of Surface Morphology Variation of CeO2(111) with Changing Annealing Condition

Cited by 8 publications

References 35 publications

STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

Epitaxial growth of CeO2(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

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

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Scanning Tunneling Microscope Study of Surface Morphology Variation of CeO₂(111) with Changing Annealing Condition