Volume 111, Issue 13, 01 October 1999
Index of content:
- SURFACES, INTERFACES, AND MATERIALS
111(1999); http://dx.doi.org/10.1063/1.479901View Description Hide Description
Magnetic circular dichroism(MCD) of trivalent rare earth dopedlithium niobate crystals is reported for the first time. Magneto-optical signals of and ions have been studied at 2 K as a function of the magnetic field strength up to 5 T. This study allows the identification of the Zeeman sublevels of these ions, which can be labeled by irreducible representations or so that the sign and allowance of transitions can be predicted. From the dependence of suitable MCD spectral lines on the magnetic field strength, the effective gyromagnetic factor of the ground state has been determined for both ions: and;
111(1999); http://dx.doi.org/10.1063/1.479902View Description Hide Description
An extension of the singlet-level equations for the density profile to the case of adsorption of polydisperse fluids on solid surfaces is presented. Explicit calculations and comparisons with canonical ensemble Monte Carlo data have been performed for a polydisperse hard sphere fluid in contact with a hard wall by using the Percus–Yevick, hypernetted chain, and a modified Verlet approximation. A numerical solution of the density profile equations makes use of the orthonormal polynomials with the weight function corresponding to the distribution function of the diameters of fluid particles.
Hydride nucleation and formation of hydride growth centers on oxidized metallic surfaces—kinetic theory111(1999); http://dx.doi.org/10.1063/1.479903View Description Hide Description
The initial stage of hydrogen–metal reactions leading to the formation of metallic hydrides, frequently proceeds (on massive metallic samples) by the appearance of hydride “spots” (or “patches”) on the surface of the metal. These spots (henceforth denoted as growth centers, GC’s) grow at a certain velocity, overlap, and finally cover the whole surface by a hydride layer (which continues to thicken into the bulk of the metal). In certain systems it has experimentally been verified that the total available number of such GC’s is limited to a certain fixed number (typical to the given metallic surface and the reaction conditions). The kinetics of formation of these GC’s is characterized by a rate function which depends on the reaction conditions, i.e., temperature and pressure, and on the metal surface characteristics. Qualitatively, these rate functions initially accelerate, reach a maximum rate, and finally decay to zero. In the present article, a kinetic theory, which accounts for that behavior, is proposed. The model assumes that the initiation of the growth process can take place only at certain sites, with a limited number of such sites available on the surface. Also, the probability for the start-up of the growth process increases with increasing supersaturation of the hydrogen concentration at these sites. The interplay between these two factors (i.e., available GC’s sites and local hydrogen concentrations) reproduces the observed kinetics of formation of the GC’s. Analytical expressions for these rate functions are derived and compared with the experimental kinetic data reported for some metal–hydrogen systems. Universal forms of the rate function and its parameters provide a simple procedure for the evaluation of specific kinetic parameters from experimentally available data.