Leed studies on the low index faces of copper

Reid, R. J.

doi:10.1016/0039-6028(72)90241-5

Cited by 47 publications

(6 citation statements)

References 14 publications

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“…Molecules at the free-surface have fewer nearest neighbors as compared to those in the bulk and, therefore, within the context of a simple ball and spring model of a solid would experience less restoring force per unit displacement. Increased vibrational amplitudes at the free-interface have been observed both experimentally and theoretically for many bulk solids. − The increased vibrational amplitudes have been shown to persist over 5 molecular layers into the surface 52 (Note our 2.9 nm is around 7 molecules). The increase in vibrational motion of the molecules near the surface could cause an observed decrease in T g .…”

Section: Discussionmentioning

confidence: 91%

Nanometer-Resolved Interfacial Fluidity

et al. 2003

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Confined liquids can have properties that are poorly predicted from bulk parameters. We resolve with 0.5 nm resolution the nanoscale perturbations that interfaces cause on fluidity, in thin 3-methylpentane (3MP) films. The films of glassy 3MP are much less viscous at the vacuum-liquid interface and much more viscous at the 3MP-metal interface, compared to the bulk of the film. We find that the viscosity at the interfaces continuously returns to the bulk value over about a 3 nm distance. The amorphous 3MP films are constructed using molecular beam epitaxy on a Pt(111) substrate at low temperatures (<30 K). Ions are gently inserted at specific distances from the substrate with a 1 eV hydronium (D(3)O(+)) or Cs(+) ion beam. The voltage across the film, which is directly proportional to the position of the ions within the film, is monitored electrostatically as the film is heated at a rate of 0.2 K/s. Above the bulk glass transition temperature (T(g)) of 3MP (77 K), the ions are expected to begin to move down through the film. However, ion movement is observed at temperatures as low as 50 K near the vacuum interface, well below the bulk T(g). The fitted kinetics predict that at 85 K, the glass is about 6 orders of magnitude less viscous near the free interface compared to that of the bulk.

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Section: Discussionmentioning

confidence: 91%

Nanometer-Resolved Interfacial Fluidity

et al. 2003

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“…The influence of thermal vibrations at surfaces on the intensities in low energy electron diffraction (LEED) has long been recognized [1,2], but so far its impact on structural analysis has found only little attention. Usually the concept of an effective Debye-Waller factor characterized by a Debye temperature 0 is introduced as a correction to relate the scattering amplitudes with thermal vibrations [3,4].…”

Section: Anisotropic Atomic Motions In Structural Analysis By Low Enementioning

confidence: 99%

Anisotropic atomic motions in structural analysis by low energy electron diffraction

Over¹,

1993

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The structure of the V3xV3/?30° overlayer formed by CO molecules adsorbed on a Ru(0001) was analyzed by low energy electron diffraction. Anisotropic atomic motions under the influence of thermal excitation were taken into account by adopting the concept of split positions. Apart from considerable improvement in the structural refinement this technique provides information about dynamic processes. In particular, the molecular axis of the CO molecules was found to be tilted on the average by (12 ± 3)° at 150 K, which is attributed to excitation of the bending mode vibration (i.e., frustrated translation).PACS numbers: 68.35.Bs, 61.14.Hg, 68.45.DaThe influence of thermal vibrations at surfaces on the intensities in low energy electron diffraction (LEED) has long been recognized [1,2], but so far its impact on structural analysis has found only little attention. Usually the concept of an effective Debye-Waller factor characterized by a Debye temperature 0 is introduced as a correction to relate the scattering amplitudes with thermal vibrations [3,4]. If one assumes isotropic and uncorrelated displacements of the atoms, this concept leads to temperature-dependent phase shifts for the scattering of electrons in the multiple-scattering theory. In LEED structural analysis the Debye temperature 0 (which usually depends markedly on energy) may be treated as an additional fit parameter or is even kept constant. This approach works remarkably well in the LEED structural analysis of clean surfaces or simple adsorbate systems as demonstrated with numerous systems [5]. However, it is certainly a strong oversimplification since vibrations at surfaces are definitely anisotropic, in particular if these are adsorbate covered, and hence the several examples that exist in the literature with relatively poor agreement between experimental and calculated LEED intensity-voltage curves (as quantified by the resulting r factors) most likely have to be attributed to such an effect [6,7]. This conclusion is supported by comparison with x-ray structure analysis where low r factors and high accuracy of the structural data can only be reached by introduction of anisotropic or even anharmonic vibrations. For surface-sensitive diffraction techniques with dominant single-scattering events these effects have been partly involved [8-10].The first approach to take account of the influence of anisotropic vibrations on the LEED intensities was to multiply the layer scattering matrices with anisotropic temperature factors [11]. Further attempts to include anisotropic vibrations in intralayer multiple scattering were made by renormalization of the single-site scattering t matrix via an anisotropic Debye-Waller factor [12]. The applicability of this approach has not yet been sufficiently investigated.It is evident that proper inclusion of anisotropic temperature effects in the calculations of LEED intensities would improve the quality of structural refinements. Moreover, this approach might even provide additional information on the dynamics beyond that ...

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“…Taking into account that the data corresponding to the (3 √ 2 × √ 2)R45 • phase were measured at room temperature (T = 300 K), and using literature values for θ D (reference [42] for Cu and [28] for last-layer Sn), we can estimate the temperature factors for our model. Table 1 shows the estimated values for B, which are used as input for the fitting process.…”

Section: Temperature Factorsmentioning

confidence: 99%

Widths and cowidths of Hardy spaces

Farkov¹

1994

Russ. Math. Surv.

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The application of genetic algorithms to the analysis of surface x-ray diffraction data is discussed and the implementation of a genetic algorithm of evolutionary type is described in detail. The structure of Sn/Cu(100)-(3 √ 2 × √ 2)R45 • is determined on the basis of surface x-ray diffraction data analysed using this algorithm. The results are compared to previous findings using other techniques.

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Leed studies on the low index faces of copper

Cited by 47 publications

References 14 publications

Nanometer-Resolved Interfacial Fluidity

Nanometer-Resolved Interfacial Fluidity

Anisotropic atomic motions in structural analysis by low energy electron diffraction

Widths and cowidths of Hardy spaces

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