Literatur

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Untersuchungen über die Thermalquellen von Wiesbaden und deren Radioaktivität

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über die Constitution des Mononitrosoorcins

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Thermal faceting of (110) and (111) surfaces of MgO

Using LEED, we have observed the thermal faceting of MgO (110) and (111) surfaces into sets of (100) faces. Some faceting occurs under ion bombardment at room temperature, and annealing at 900–1400 K by means of electron bombardment produces complete faceting, with facets up to 1 μm across. These observations are consistent with theories of the stability of ionic crystal surfaces.     

The nature of transition-metal-oxide surfaces

The surfaces of the 3d-transition-metal oxides form a rich and important system in which to study the effects of atomic geometry, ligand coordination and d-orbital population on surface electronic structure and chemisorption. This article considers the properties of those surfaces in terms of the types of surface structures that can exist, including steps and point defects, and their relation to the experimental data that is available for well characterized, single-crystal surfaces. The electronic structure of nearly perfect surfaces is very similar to that of the bulk for many of the oxides that have been studied; atoms at step sites also appear to have properties similar to those of atoms on terraces. Point defects are often associated with surfaces 0 vacancies and attendant transfer of electrons to adjacent metal cations. Those cations are poorly screened from each other, and the excess charge is presumably shared between two or more cations having reduced ligand coordination. Point defects are generally more active for chemisorption than are perfect surfaces, however for Ti₂O₃ and V₂O₃, whose cations have 3d¹ and 3d² electronic configurations respectively, the cleaved (047) surface is more active than are surfaces having a high density of defects. The chemisorption behavior of both nearly perfect and defect surfaces of 3d-transition-metal oxides varies widely from one material to another, and it is suggestive to correlate this with cation d-orbital population. However, too few oxides have yet been studied to draw any firm conclusions. Additional theoretical work on perfect surfaces, defects and chemisorption is also necessary in order to gain a more complete understanding of transition-metal-oxide surfaces.     

Differential sputtering of MgO/Au cermet films and its application to high-yield secondary-electron emitters

Very large differential-sputtering effects in fine-grained (particle size < 50 Å) MgO/Au cermet films have been observed by Auger electron spectroscopy. Under Ar-ion bombardment, the surface Au content was found to decrease exponentially with time by up to a factor of 20. A theoretical model for differential sputtering of granular systems is presented that gives good agreement with the experimental data. The differential sputtering produces a MgO-rich surface layer and therefore results in excellent secondary-electron-emission properties for low-energy incident electrons.     

Molecular simulation of LiCl aqueous solutions

Non-primitive LiCl aqueous electrolyte solutions were studied at 1.0, 5.0 and 10.0 M concentrations by molecular dynamics simulations. It was observed that the ion hydration structure is progressively lost with increasing concentration. The ions are aggregated in small clusters at C = 1.0 M. However, at this concentration, two large clusters were detected that are an initial step in an aggregation process. At C = 5.0 M, the highly unstable ion clustering seems to correspond to an intermediary state between low concentration states with poor aggregation and states where the ions are highly aggregated, as observed at C = 10.0 M where almost all the ions are clustered in one cluster. This cluster does not present a crystal-like structure. The high solubility of LiCl in aqueous solutions can consequently be explained as a result of the large radii difference between the anion and the cation that results in the instability of the ionic aggregates, which makes the formation of crystal seeds difficult.