Structure and phase stability of nanocrystalline Ce1−xLnxO2−x/2−δ (Ln = Yb, Lu) in oxidizing and reducing atmosphere

The structure and phase evolution of nanocrystalline Ce1−xLnxO2−x/2−δ (Ln = Yb, Lu, x = 0 − 1) oxides upon heating in H2 was studied for the first time. Up to 950 °C the samples were single-phase, with structure changing smoothly with x from fluorite type (F) to bixbyite type (C). For the Lu-doped samples heated at 1100 °C in the air and H2, phase separation into coexisting F- and C-type structures was observed for ~0.40 < x < ~0.70 and ~0.25 < x < ~0.70, respectively. It was found also that addition of Lu3+ and Yb3+ strongly hinders the crystallite growth of ceria during heat treatment at 800 and 950 °C in both atmospheres. Valency of Ce and Yb in Ce0.1Lu0.9O1.55−δ and Ce0.95Yb0.05O1.975−δ samples heated at 1100 °C was studied by XANES and magnetic measurements. In the former Ce was dominated by Ce4+, with small contribution of Ce3+ after heating in H2. In the latter, Yb existed exclusively as 3+ in both O2 and H2

BOOST PERFORMANCE OF MILLIMETER-WAVE QUANTUM-WELL DEVICES

X110sci

MILLIMETER-WAVE POWER OPERATION OF AN ALGAAS/INGAAS/GAAS QUANTUM WELL MISFET

X1127sciescopu

The international VAMAS project on X-ray reflectivity measurements for evaluation of thin films and multilayers - Preliminary results from the second round-robin

X-ray reflectometry (XRR) is a unique technique for thin film analysis providing information on thickness, density, and roughness. The Versailles Project on Advanced Materials and Standards (VAMAS) project "X-ray reflectivity measurements for evaluation of thin films and multilayers" has the goal to assess the accuracy and precision of thickness, density and roughness as determined by XRR measurements and simulations. Here we present preliminary results from the second round-robin analysis on a TaN/Ta metallization on a silicon substrate. This work demonstrated a good inter-laboratory reproducibility for the tantalum film thickness with a standard deviation of 0.04 nm corresponding to about 0.3%. The use of the auto-correlation function (extracted from the derivative of density profiles obtained via a Fourier transform) was found to provide useful layer thickness measurements from important samples that are too complex for a simple direct simulation and fitting approach. © 2008 Elsevier B.V. All rights reserved

Anomalous small-angle x-ray scattering from mesoporous noble metal catalysts

We present the analysis of a catalyst containingplatinum nanoparticles supported on mesoporous MCM-41silica by anomalous small-angle x-ray scattering (ASAXS).The analysis of this composite system by ASAXS is firststudied by use of model calculation. Here, it is shown thatthe full analysis must proceed by decomposing the scatteringdata measured at different energies of the incident beam intothree partial intensities. This evaluation is compared to asimplified method in which scattering curves measured attwo different energies are subtracted from each other. Thedifferent methods are applied to experimental data obtainedfrom platinum nanoparticles on anMCM-41 support material.The model calculations show that the simplified method leadsto large deviations especially at low q in ordered systems. Inthe semi-ordered material MCM-41, these deviations are lesspronounced, and the method of simple subtraction proves tobe a good approximation for q values higher than 0.1 nm−1