Defect Structure of Ultrathin Ceria Films on Pt(111): Atomic Views from Scanning Tunnelling Microscopy

Grinter, David C.; Ithnin, R.; Pang, Chi L.; Thornton, G.

doi:10.1021/jp102895k

Cited by 102 publications

(149 citation statements)

References 31 publications

Supporting

Mentioning

131

Contrasting

Order By: Relevance

“…7 A seminal experimental study 8 proposed that O vacancies cluster together. Notwithstanding one theoretical study supporting this 9 , other experimental [10][11][12] and theoretical 6,13,14 works suggest that lattice relaxation effects cause vacancies to repel each other, with the prior experimental evidence for vacancy clustering being attributed to fluorine contamination of the ceria crystal 12 . Connected with the formation of O vacancies is the localization of the extra electrons.…”

Section: Introductionmentioning

confidence: 77%

Origins and implications of the ordering of oxygen vacancies and localized electrons on partially reducedCeO2(111)

2015

View full text Add to dashboard Cite

We use density functional theory to explain the preferred structure of partially reduced CeO 2 (111). Low energy ordered structures are formed when the vacancies are isolated (maximized intervacancy separation) and the size of the Ce 3+ ions is minimized. Both conditions help minimize disruptions to the lattice around the vacancy. The stability of the ordered structures suggests that isolated vacancies are adequate for modeling more complex (e.g., catalytic) systems. O diffusion barriers are predicted to be low enough that O diffusion between vacancies is thermodynamically controlled at room temperature. The O diffusion reaction energies and barriers are decreased when one Ce f electron hops from a nearest neighbor Ce cation to a next nearest neighbor Ce cation, with a barrier that has been estimated to be slightly less than the barrier to O diffusion in the absence of polaron hopping. This indicates that polaron hopping plays a key role in facilitating the overall O diffusion process, and depending on the relative magnitudes of the polaron hopping and O diffusion barriers, polaron hopping may be the kinetically limiting process.

show abstract

Section: Introductionmentioning

confidence: 77%

Origins and implications of the ordering of oxygen vacancies and localized electrons on partially reducedCeO2(111)

2015

View full text Add to dashboard Cite

show abstract

“…14, 16 We suspect that tunneling out of the O 2p orbitals is hindered by the limited mobility of ceria electrons at the cryogenic temperature used in our experiment. The film thickness was varied between one and six O-Ce-O trilayers, corresponding to 3-18 Å .…”

Section: Methodsmentioning

confidence: 93%

“…12 Oxygen vacancies in surface and subsurface ceria layers have been extensively studied with STM and scanning force microscopy, revealing the defect position in the oxide lattice and the associated relaxations of neighboring ions. [13][14][15][16] The vacancies are mainly generated with two approaches, namely thermal treatment of the oxide to stimulate oxygen desorption 13,14 and electron bombardment. 17 In both cases, they were exclusively observed on plain oxide terraces, although DFT calculations found the defect-formation energy to be substantially lowered at low-coordinated step and corner sites.…”

Section: Introductionmentioning

confidence: 99%

Probing the 4f states of ceria by tunneling spectroscopy

Shao

Jerratsch

Nilius

et al. 2011

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

Low-temperature scanning tunneling microscopy and spectroscopy have been employed to analyze the local electronic structure of the (111) surface of a ceria thin film grown on Ru(0001). On pristine, defect-free oxide terraces, the empty 4f states of Ce 4+ ions appear as the only spectral feature inside the 6 eV oxide band gap. In contrast, occupied states are detected between À1.0 and À1.5 eV below E Fermi in conductance spectra of different point and line defects, such as surface oxygen vacancies, grain boundaries and step edges. They are assigned to partially filled 4f states localized at the Ce 3+ ions. The presence of excess electrons indicates the oxygen-deficient nature of the direct oxide environment. The f state spectroscopy with the STM allows us to probe the spatial distribution of Ce 3+ ions in the ceria surface, providing unique insight into the local reduction state of this chemically important material system.

show abstract

“…More explicitly, calculations predict that the vacancy is more stable in the subsurface layer than in the surface layer [14], which would suggest that the number of surface defects should decrease with annealing time; that its diffusion barrier is small [15], which would render it highly mobile at the elevated temperatures at which the experiments were carried out; and that clustering of surface vacancies is energetically unfavourable [16], implying that they should exist primarily in isolation. Despite the doubt cast by these inconsistencies upon the interpretation of the defect structure of CeO 2 ð111Þ in terms of oxygen vacancies alone, no alternative model has been proposed, and numerous authors have subsequently used the "vacancy model" to interpret the results of their experiments, based both on STM and on other techniques [17][18][19][20].…”

mentioning

confidence: 99%

Oxygen Vacancies versus Fluorine atCeO2(111): A Case of Mistaken Identity?

et al. 2014

View full text Add to dashboard Cite

We propose a resolution to the puzzle presented by the surface defects observed with STM at the (111) surface facet of CeO 2 single crystals. In the seminal paper of Esch et al. [Science 309, 752 (2005)] they were identified with oxygen vacancies, but the observed behavior of these defects is inconsistent with the results of density functional theory (DFT) studies of oxygen vacancies in the literature. We resolve these inconsistencies via DFT calculations of the properties of both oxygen vacancies and fluorine impurities at CeO 2 ð111Þ, the latter having recently been shown to exist in high concentrations in single crystals from a widely used commercial source of such samples. We find that the simulated filled-state STM images of surface-layer oxygen vacancies and fluorine impurities are essentially identical, which would render problematic their experimental distinction by such images alone. However, we find that our theoretical results for the most stable location, mobility, and tendency to cluster, of fluorine impurities are consistent with experimental observations, in contrast to those for oxygen vacancies. Based on these results, we propose that the surface defects observed in STM experiments on CeO 2 single crystals reported heretofore were not oxygen vacancies, but fluorine impurities. Since the similarity of the simulated STM images of the two defects is due primarily to the relative energies of the 2p states of oxygen and fluorine ions, this confusion might also occur for other oxides which have been either doped or contaminated with fluorine.

show abstract

Defect Structure of Ultrathin Ceria Films on Pt(111): Atomic Views from Scanning Tunnelling Microscopy

Cited by 102 publications

References 31 publications

Origins and implications of the ordering of oxygen vacancies and localized electrons on partially reducedCeO2(111)

Origins and implications of the ordering of oxygen vacancies and localized electrons on partially reducedCeO2(111)

Probing the 4f states of ceria by tunneling spectroscopy

Oxygen Vacancies versus Fluorine atCeO2(111): A Case of Mistaken Identity?

Contact Info

Product

Resources

About