Improvement of the properties of CSD-processed (Pb0.76Ca0.24)TiO3 thin films by control of the solution chemistry

Ferroelectric (Pb_0.76Ca_0.24)TiO₃ thin films were prepared on platinized Si substrates by chemical solution deposition (CSD). Two different synthetic strategies were adopted to optimize the functionality of the resulting perovskite films: (1) tailoring the schedule of the solution synthesis and (2) chemical selectivity of the calcium precursor. The choice of an appropriate synthetic procedure led to homogeneous sols constituted by a single distribution of particles, as revealed by dynamic light scattering (DLS). Stronger polymeric structures in the sol network are believed to prevent atomic diffusion of metal cations during crystallization at higher temperatures, and perovskite films with a uniform compositional profile and without any detrimental interface with the electrode were measured by Rutherford backscattering spectroscopy (RBS). On the other hand, phase formation and microstructure of crystalline films were strongly affected by the calcium compound used, i.e. calcium acetate or calcium acetylacetonate. The single decomposition mechanism of the last one, with absence of intermediate carbonates, resulted in the prompt crystallization of the perovskite phase (375°C) and an enhanced grain-growth mechanism that led to dense films formed by larger grains. Consequently, the optimized ferroelectric (Pb_0.76Ca_0.24)TiO₃ films showed superior electrical properties: maximum values of dielectric constant nearly doubled and a relative increase in the remanent polarization being ∼40% (P _r =23 μC/cm²). The potential application of these films in functional microelectronic devices is also demonstrated.     

Spectral image cathodoluminescence,photoluminescence and Raman study of GaAs layers grown on Si substrates

GaAs layers grown on Si substrates by the conformal method were investigated by means of Raman, photoluminescence and cathodoluminescence spectroscopies. The combination of these optical techniques allows a better knowledge of the properties of these layers, with special emphasis on the stress distribution and the incorporation of dopants. In particular, samples intentionally doped, with alternate doped and undoped fringes, have been analyzed. The effective incorporation of Si atoms in the GaAs structure to produce n-type layers and the formation of Si complexes are determined by Raman and cathodoluminescence data. The lateral quasi-periodic stress distribution, typically observed in these layers, is shown to affect the Si incorporation.     

Chemical investigation of three plutonium–beryllium neutron sources

Thorough physical and chemical characterization of plutonium–beryllium (PuBe) neutron sources is an important capability with applications ranging from material accountancy to nuclear forensics. Characterization of PuBe sources is not trivial owing to range of existing source designs and the need for adequate infrastructure to deal with radiation and protect the analyst. This study demonstrates a method for characterization of three PuBe sources that includes physical inspection and imaging followed by controlled disassembly and destructive analysis.