Atomic Resolution Imaging of the (001) Surface of UHV Cleaved MgO by Dynamic Scanning Force Microscopy

Barth, Clemens; Henry, Claude R.

doi:10.1103/physrevlett.91.196102

Cited by 151 publications

(138 citation statements)

References 28 publications

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“…For example, AFM images shown in fig. 1 in Barth & Henry (2003) demonstrate that irregular adstructures, reminiscent of debris on the rough surface shown in figure 6, are formed alongside well-defined rectangular pits of monoatomic depth.…”

Section: (B) Surface Structuresmentioning

confidence: 99%

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al ₂ O ₃

et al. 2011

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Surface structures of stoichiometric and oxygen-deficient complex subnanoporous oxide 12CaO·7Al 2 O 3 (C12A7) are generated by simulating lattice rupture under the influence of an external strain. Extra-framework anions are found to serve as buffers, maintaining stability of the lattice cages in both elastic and inelastic stretching regimes. Modification of the local atomic structure in the near-surface region reduces the band gap in stoichiometric insulating C12A7. On the contrary, the band gap appears in the oxygendeficient form of C12A7, which is metallic in the bulk. This is due to formation of the surface electron traps, which differ both in the type of the local atomic structure and stability of the electronic states. The implications of this electronic structure for the surface chemical and electron emission properties are discussed.

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Section: (B) Surface Structuresmentioning

confidence: 99%

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al ₂ O ₃

et al. 2011

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“…Atomic force microscopy (AFM) studies operated in the so-called noncontact mode (NC-AFM) have recently been successfully employed for atomic-scale studies of a range of clean metal oxide insulating surfaces, [17][18][19] such as α-Al 2 O 3 (0001) [20][21][22] or MgO. 23,24 Very recently, we used NC-AFM to resolve the atomic-scale surface structure of the MgAl 2 O 4 (100) surface. 7 The studies in Ref.…”

Section: Introductionmentioning

confidence: 99%

Noncontact atomic force microscopy imaging of atomic structure and cation defects of the polar MgAl2O4(100) surface: Experiments and first-principles simulations

et al. 2011

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version of the following article: Rasmussen, Morten K. ; Foster, Adam S. ; Canova, Filippo F. ; Hinnemann, Berit ; Helveg, Stig ; Meinander, Kristoffer ; Besenbacher, Flemming ; Lauritsen, Jeppe V.. 2011. Noncontact atomic force microscopy imaging of atomic structure and cation defects of the polar MgAl2O4 (100) All material supplied via Aaltodoc is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Atom-resolved noncontact atomic force microscopy (NC-AFM) was recently used to reveal that the insulating spinel MgAl 2 O 4 (100) surface, when prepared under vacuum conditions, adopts a structurally well-defined Al and O-rich structure (Al 4 -O 4 -Al 4 termination) consisting of alternating Al and double-O rows, which are, however, interrupted by defects identified as interchanged Mg in the surface layers (so-called antisite defects). From an interplay of futher NC-AFM experiments and first-principles NC-AFM image simulations, we present here a detailed analysis of the NC-AFM contrast on the MgAl 2 O 4 (100) surface. Experiments show that the contrast on MgAl 2 O 4 (100) in atom-resolved NC-AFM is dominated by two distinctly different types of contrast modes, reflecting two oppositely charged tip-apex terminations. In this paper, we analyze the contrast associated with these imaging modes and show that a positively charged tip-apex (presumably Mg 2+ ) interacts most strongly with the oxygen atoms, thus imaging the oxygen lattice, whereas a negatively charged tip-apex (O 2− ) will reveal the cation sublattice on MgAl 2 O 4 . The analysis of force-vs-distance calculations for the two tips shows that this qualitative picture, developed in our previous study, holds for all realistic tip-surface imaging parameters, but the detailed resolution on the O double rows and Al rows changes as a function of tip-surface distance, which is also observed experimentally. We also provide an analysis of the tip dependency and tip-surface distance dependency for the NC-AFM contrast associated with single Al vacancies and Mg-Al antisite defects on the MgAl 2 O 4 (100) surface and show that it is possible on the basis of NC-AFM image simulations to discriminate between the Al 3+ and Mg 2+ species in antisite defects and hypothetical Al vacancies.

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“…This is a clear indication that defects play an important role in the growth process. It is well known that oxide surfaces tend to have a high density of point defects (typical estimates being 10 12 -10 13 cm À2 [31]) in addition to steps and grain boundaries. HREELS spectra have been assigned and interpreted in terms of neutral oxygen vacancies, so called F-centers, where an oxygen atom has been removed from the surface [32].…”

Section: Introductionmentioning

confidence: 99%

“…HREELS spectra have been assigned and interpreted in terms of neutral oxygen vacancies, so called F-centers, where an oxygen atom has been removed from the surface [32]. It has also been suggested that di-vacancies are present where both a Mg-and O-atom are missing [31] and, in some cases, charged oxygen vacancies [32,33]. We have assumed that the defects nucleating Pd clusters are neutral oxygen vacancies.…”

Section: Introductionmentioning

confidence: 99%

Pd diffusion on MgO(100): The role of defects and small cluster mobility

Henkelman

Campbell

et al. 2006

Surface Science

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Density functional theory is used to explore the energy landscape of Pd atoms adsorbed on the terrace of MgO(1 0 0) and at oxygen vacancy sites. Saddle point finding methods reveal that small Pd clusters diffuse on the terrace in interesting ways. The monomer and dimer diffuse via single atom hops between oxygen sites with barriers of 0.34 eV and 0.43 eV respectively. The trimer and tetramer, however, form 3D clusters by overcoming a 2D-3D transition barrier of less than 60 meV. The trimer diffuses along the surface either by a walking or flipping motion, with comparable barriers of ca. 0.5 eV. The tetramer rolls along the terrace with a lower barrier of 0.42 eV. Soft rotational modes at the saddle point lead to an anomalously high prefactor of 1.3 · 10 14 s À1 for tetramer diffusion. This prefactor is two order of magnitude higher than for monomer diffusion, making the tetramer the fastest diffusing species on the terrace at all temperatures for which diffusion is active (above 200 K). Neutral oxygen vacancy sites are found to bind Pd monomers with a 2.63 eV stronger binding energy than the terrace. A second Pd atom, however, binds to this trapped monomer with a smaller energy of 0.56 eV, so that dimers at defects dissociate on a time scale of milliseconds at room temperature. Larger clusters bind more strongly at defects. Trimers and tetramers dissociate from monomer-bound-defects at elevated temperatures of ca. 600 K. These species are also mobile on the terrace, suggesting they are important for the ripening observed at P600 K during Pd vapor deposition on MgO(1 0 0) by Haas et al.

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Atomic Resolution Imaging of the (001) Surface of UHV Cleaved MgO by Dynamic Scanning Force Microscopy

Cited by 151 publications

References 28 publications

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al ₂ O ₃

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al ₂ O ₃

Noncontact atomic force microscopy imaging of atomic structure and cation defects of the polar MgAl2O4(100) surface: Experiments and first-principles simulations

Pd diffusion on MgO(100): The role of defects and small cluster mobility

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Atomic Resolution Imaging of the (001) Surface of UHV Cleaved MgO by Dynamic Scanning Force Microscopy

Cited by 151 publications

References 28 publications

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al 2 O 3

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al 2 O 3

Noncontact atomic force microscopy imaging of atomic structure and cation defects of the polar MgAl2O4(100) surface: Experiments and first-principles simulations

Pd diffusion on MgO(100): The role of defects and small cluster mobility

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Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al ₂ O ₃

Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al ₂ O ₃