[en] A general probabilistic technique for estimating background contributions to measured spectra is presented. A Bayesian model is used to capture the defining characteristics of the problem, namely, that the background is smoother than the signal. The signal is allowed to have positive and/or negative components. The background is represented in terms of a cubic spline basis. A variable degree of smoothness of the background is attained by allowing the number of knots and the knot positions to be adaptively chosen on the basis of the data. The fully Bayesian approach taken provides a natural way to handle knot adaptivity and allows uncertainties in the background to be estimated. Our technique is demonstrated on a particle induced x-ray emission spectrum from a geological sample and an Auger spectrum from iron, which contains signals with both positive and negative components. (c) 2000 The American Physical Society

[en] The light rare-earth metal, neodymium, has been studied up to 155 GPa in a diamond-anvil cell using energy dispersive x-ray diffraction with a synchrotron source. The pressures were calibrated using copper as an internal x-ray pressure standard. A phase transformation from a monoclinic phase (C2/m, 4 atoms/cell) to an orthorhombic α-U phase (Cmcm, 4 atoms/cell) was observed at 113±6 GPa without any observable volume collapse. The observation of α-U phase in Nd and, previously, in cerium and praseodymium clearly establishes this phase in light rare-earth metals. Our equation of state measurements suggest that delocalization of the f shell in Nd occurs without any volume collapse unlike Ce and Pr. (c) 2000 The American Physical Society

[en] In order to overcome dissipation due to impurity segregation at grain boundaries, niobium cavities are submitted to a purification annealing (1300 degree C±200 degree C under vacuum) during which titanium is evaporated onto the Nb surface. The resulting titanium layer acts as a solid state getter reacting with light impurities (H, C, N, O), thereby removing these impurities from the bulk of the niobium. Preferential titanium diffusion along grain boundaries have been studied using proton-induced x-ray emission. copyright 1997 American Institute of Physics

[en] The fabrication of nonvolatile ferroelectric random access memories based on SrBi₂Ta₂O₉ (SBT) or other ferroelectric capacitors require exposure of these capacitors to processing gases mixtures including hydrogen. This results in a strong degradation of the capacitor electrical properties, mainly due to the interaction of hydrogen with the ferroelectric layer. Using surface analysis methods, we previously determined that the hydrogen-induced degradation of SBT capacitors might be partially due to the degradation of the near surface region of the SBT layer. It was also demonstrated that oxygen annealing after the hydrogen exposure results in the recovery of the degraded SBT surface layer and the electrical properties of the capacitor. We have now performed detailed cross sectional transmission electron microscopy studies of virgin, hydrogen, and oxygen annealed SBT/Pt/TiO₂/SiO₂/Si heterostructures. These studies combined microstructural imaging with a nanoscale compositional analysis of the SBT layer as a function of depth from the free surface of the film and across grain boundaries. High resolution energy dispersive x-ray spectroscopy revealed that hydrogen annealed SBT layers have a deficiency of Bi up to a depth of ∼30 nm underneath the free surface, and that there is accumulation of Bi at the grain boundaries of pristine, hydrogen, and oxygen-recovery annealed SBT layers. This suggests that the diffusion of Bi is largely controlled by grain boundaries and they play a critical role in controlling the electrical properties of SBT capacitors. (c) 2000 American Institute of Physics