[en] Highlights: • Interfacial water forms cubic-ice crystallites with a {1 1 0}-preferred orientation. • Four stages of ultrafast structural dynamics of interfacial water are presented. • A nonequilibrium isotropic phase transformation of interfacial ice is identified. • Cooperativity of a hydrogen-bonded network inhibits sublimation during large motions. Using time-averaged and ultrafast electron diffraction, structures and ultrafast dynamics of interfacial water assemblies on smooth hydrophobic surfaces are reported. The lack of hydrophilic interaction and topographical template effect from the support surface leads to the formation of small, mostly randomly-oriented, ice crystallites with the cubic structure. Dynamically, following the substrate photoexcitation, interfacial water assemblies undergo four stages of changes—ultrafast melting, nonequilibrium isotropic phase transformation, annealing, and restructuring—which are closely correlated with the substrate dynamics. The connectivity and cooperative nature of the hydrogen-bonded network is considered crucial for water assemblies to withstand large structural motions without sublimation on ultrashort times.

[en] The basic ideas and possibilities of application of Low Energy Electron Diffraction (L.E.E.D.) are briefly reviewed. The geometry of the diffraction pattern is due to conservation rules together with the periodicity of the crystal surface. The intensity of the diffracted beams is governed by the electron-solid interaction and the multiple scattering effects. The muffin-tin model allows us to split the problem into four parts: scattering by ion-cores; propagation in a constant potential medium, accounting for the many body interactions of the electron with the electron gas; scattering by the surface potential barrier; self-consistent calculation of the effective wave fields. Possibilities of application are large. L.E.E.D. is a powerful method for surface characterization, sensitive to long range order. It is a necessary complement to the methods suited for the chemical determination of the atoms on a surface, such as Auger electron spectroscopy of X-ray photoelectron spectroscopy. Applications to surface crystallography are still limited to simple superstructures. The analyses are far too much expensive. A suitable choice of the experimental basis should probably reduce their cost to a level manageable for many laboratories

[en] Steps presence on vicinal surfaces changes the low energy electron difraction (LEED) pattern: a system of regulary spaced steps is causing some spots to be splitted. Using a high voltage LEED apparatus allows an easy explanation of the patterns: the spot position does not depend about energy and so some cristallographic parameters can be easily measured

[en] Being an independent method of structure analysis, electron diffraction provides original data which are essential contributions to all the fields where this method is used. An important place of electron diffraction among other structural methods is illustrated by the results of the studies once started on clay minerals and continued on the objects extremely important for structural mineralogy, which stimulated the development of a new field - modular crystallography

[en] The electron diffraction pattern for two-slits with magnetic flux confined to an inaccessible region between them is calculated. The Aharonov-Bohm effect gives a diffraction pattern which is asymmetric but with a symmetric envelope. In general, both expected displacement and kinetic momentum of the electron are nonzero as a consequence of the asymmetry. Nevertheless Ehrenfest's theorems and the conservation of momentum are satisfied. (author)

[en] By the materials of the lecture delivered in the School on Electron Crystallography, Erice, Sicily, 1997 and published in Proceedings of NATO Advanced Study Institute on Electron Crystallography, Erice, Sicily, 1997, Series E, vol. 347, p. 1

No abstract available

[en] A wave approach of electron scattering by crystals is presented. A notion of coherence between the Bloch waves components is introduced. The first results, in agreement with the existing theories, permit the interpretation of the contrast of diffraction patterns

[en] A Bloch-wave analysis is made of the problem of uncoupling surface superlattice reflections from fundamental reflections in transmission electron diffraction (TED) analysis of reconstructed surfaces. This uncoupling problem is proved to be of crucial importance in determining the structure of reconstructed surfaces, for example the Si(111) 7x7 surface. It is found that a complete uncoupling, weak coupling and sometimes strong coupling between the bulk scattering and surface superlattice scattering are all possible depending on the diffraction conditions. For a kinematical analysis of reconstructed surfaces to be valid, a weak coupling or a complete uncoupling condition must be realized. General rules for choosing the appropriate diffraction conditions are given. (orig.)

[en] A general form for the intensity distribution of thermal diffuse scattering (TDS) is derived within the framework of quantum mechanics. The formulation takes into account the dynamical diffraction effects for both the initial and the final states of high-energy electrons and uses a single incoherent scattering approximation. When applied to estimate the intensity distribution of TDS in reflection high-energy electron diffraction (RHEED), using a two-wave approximation for the elastically scattered wave field, an analytical expression is obtained. It is shown that the dynamical diffraction effects may lead to an enhancement in the TDS intensities near the diffraction spots. The influence of correlated thermal atomic displacements on the contrast of the Kikuchi line parallel to the surface shadow edge has been discussed. (orig.)