Atom-resolved noncontact atomic force microscopic and scanning tunneling microscopic observations of the structure and dynamic behavior of CeO2(111) surfaces

Namai, Yoshimichi; Fukui, Ken–ichi; Iwasawa, Yasuhiro

doi:10.1016/s0920-5861(03)00377-8

Cited by 111 publications

(106 citation statements)

References 31 publications

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“…In all of these, the vacancy structures, formation energies, and diffusion barriers are very important. So far, most experimental, [1][2][3][4][5][6] and many theoretical [6][7][8][9][10] studies have considered vacancies only on the (111) surface of ceria, since experimentally this is normally the most stable, and theoretical studies using analytical force-fields (FF), [11][12][13][14][15] HF, 16 and DFT [17][18][19][20][21][22][23][24] all essentially support the experimental findings and agree on the order of stability: (111) > (110) > (100). However, it has been suggested that much of the interesting surface chemistry may be taking place not on the most stable (111) surface, but rather on other surfaces or possibly at step-edges or at other topological surface defects.…”

Section: Introductionmentioning

confidence: 73%

Many competing ceria (110) oxygen vacancy structures: From small to large supercells

Kullgren

Hermansson

Castleton

2012

The Journal of Chemical Physics

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We present periodic "DFT+U" studies of single oxygen vacancies on the CeO 2 (110) surface using a number of different supercells, finding a range of different local minimum structures for the vacancy and its two accompanying Ce(III) ions. We find three different geometrical structures in combination with a variety of different Ce(III) localization patterns, several of which have not been studied before. The desired trapping of electrons was achieved in a two-stage optimization procedure. We find that the surface oxygen nearest to the vacancy either moves within the plane towards the vacancy, or rises out of the surface into either a symmetric or an unsymmetric bridge structure. Results are shown in seven slab geometry supercells, p(2 × 1), p(2 × 2), p(2 × 3), p(3 × 2), p(2 × 4), p(4 × 2), and p(3 × 3), and indicate that the choice of supercell can affect the results qualitatively and quantitatively. An unsymmetric bridge structure with one nearest and one next-nearest neighbour Ce(III) ion (a combination of localizations not previously found) is the ground state in all (but one) of the supercells studied here, and the relative stability of other structures depends strongly on supercell size. Within any one supercell the formation energies of the different vacancy structures differ by up to 0.5 eV, but the same structure can vary by up to ∼1 eV between supercells. Furthermore, finite size scaling suggests that the remaining errors (compared to still larger supercells) can also be ∼1 eV for some vacancy structures.

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Section: Introductionmentioning

confidence: 73%

Many competing ceria (110) oxygen vacancy structures: From small to large supercells

Kullgren

Hermansson

Castleton

2012

The Journal of Chemical Physics

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“…The signal generation in AFM is based on force interactions between a local sensor tip and the surface and therefore independent of the sample conductivity. 61 This enables the investigation of insulating oxides with atomic resolution, as demonstrated for bulk CeO 2 , 62 MgO 63 and α-Al 2 O 3 , 64 as well as for alumina and magnesia thin films grown on NiAl (110), Ni 3 Al(111) and Ag(001), respectively. 65,66,67 The STM, on the other hand, probes the local density of states (LDOS) of the sample surface and therefore its electronic properties.…”

Section: Scanning Tunneling Microscopy On Oxide Surfacesmentioning

confidence: 95%

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

Nilius

2009

Surface Science Reports

221

233

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The preparation of thin oxide films on metal supports is a versatile approach to explore the properties of oxide materials that are otherwise inaccessible to most surface science techniques due to their insulating nature. Although substantial progress has been made in the characterization of oxide surfaces with spatially averaging techniques, a local view is often essential to provide comprehensive understanding of such systems. The scanning tunneling microscope (STM) is a powerful tool to obtain atomic-scale information on the growth behavior of oxide films, the resulting surface morphology and defect structure.

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“…Specifically, NC-AFM studies have identified individual surface and subsurface oxygen vacancies ( Figure 6). 35 Moreover, oxygen surface diffusion on ceria surface was observed, 39 and it was determined that water molecules dissociate on oxygen vacancies thereby filling the vacancies with hydroxyls. 40 Finally, high-resolution images of the step edges revealed predominant (110) and (001) facets, which, with theory, lead to the conclusion that CO oxidation on CeO 2 (111) mainly occurs at step edges due to enhanced chemical interaction with CO molecules.…”

Section: Nc-afm Analysis Of Catalytic Surfacesmentioning

confidence: 99%

Noncontact Atomic Force Microscopy: An Emerging Tool for Fundamental Catalysis Research

Altman¹,

Baykara

Schwarz³

2015

Acc. Chem. Res.

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CONSPECTUS:Although atomic force microscopy (AFM) was rapidly adopted as a routine surface imaging apparatus after its introduction in 1986, it has not been widely used in catalysis research. The reason is that common AFM operating modes do not provide the atomic resolution required to follow catalytic processes; rather the more complex noncontact (NC) mode is needed. Thus, scanning tunneling microscopy has been the principal tool for atomic scale catalysis research. In this Account, recent developments in NC-AFM will be presented that offer significant advantages for gaining a complete atomic level view of catalysis. The main advantage of NC-AFM is that the image contrast is due to the very short-range chemical forces that are of interest in catalysis. This motivated our development of 3D-AFM, a method that yields quantitative atomic resolution images of the potential energy surfaces that govern how molecules approach, stick, diffuse, and rebound from surfaces. A variation of 3D-AFM allows the determination of forces required to push atoms and molecules on surfaces, from which diffusion barriers and variations in adsorption strength may be obtained. Pushing molecules towards each other provides access to intermolecular interaction between reaction partners. Following reaction, NC-AFM with CO-terminated tips yields textbook images of intramolecular structure that can be used to identify reaction intermediates and products. Because NC-AFM and STM contrast mechanisms are distinct, combining the two methods can produce unique insight. It is demonstrated for surface-oxidized Cu(100) that simultaneous 3D-AFM/STM yields resolution of both the Cu and O atoms. Moreover, atomic defects in the Cu sublattice lead to variations in the reactivity of the neighboring O atoms. It is shown that NC-AFM also allows a straightforward imaging of work function variations which has been used to identify defect charge states on catalytic surfaces and to map charge transfer within an individual molecule. These advances highlight the potential for NC-AFM-based methods to become the cornerstone upon which a quantitative atomic scale view of each step of a catalytic process may be gained. Realizing this potential will rely on two breakthroughs: (1) development of robust methods for tip functionalization and (2) simplification of NC-AFM instrumentation and control schemes. Quartz force sensors may offer paths forward in both cases. They allow any material with an atomic asperity to be used as a tip, opening the door to a wide range of surface functionalization chemistry. In addition, they do not suffer from the instabilities that motivated the initial adoption of complex control strategies that are still used today.

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Atom-resolved noncontact atomic force microscopic and scanning tunneling microscopic observations of the structure and dynamic behavior of CeO2(111) surfaces

Cited by 111 publications

References 31 publications

Many competing ceria (110) oxygen vacancy structures: From small to large supercells

Many competing ceria (110) oxygen vacancy structures: From small to large supercells

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

Noncontact Atomic Force Microscopy: An Emerging Tool for Fundamental Catalysis Research

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