RESUMEN
Accurate control of residual defect density is required for reliable investigation and use of ferroelectric materials. After reviewing the long term endeavor to decrease defect contributions in bulk materials, which reached mass production decades ago, recent challenges are underlined. These mostly result from the continuous trend towards integration which has reached the nanometre range. The contribution of solid state chemistry is of key relevance for improving the present processing routes and suggesting alternative ones, for example by controlling a large density of charged defects to reach unprecedented functionalities. Some of these breakthroughs are reviewed.
RESUMEN
We have investigated the macroscopic and microscopic properties of large sets of Ba0.7Sr0.3TiO3 thin films including several substitution rates of manganese. Thanks to a high degree of control of the processing parameters at each stage we have been able to find a link between the dc leakage current and the low and high frequency dielectric permittivity and losses. We supplemented these macroscopic observations with in depth investigations of the defect states through x-ray photoelectron spectroscopy. We found that both the leakage current and the extrinsic dielectric parameters arise from a large density of charged point defects related to oxygen vacancies. At the outer surfaces of the films, the density of such charged defects is so high that it can raise the Fermi level to close to the conduction band. Such degradation of the films' performance can be relieved by appropriate manganese substitution for the titanium host ions. Such doping is able to move back the Fermi level to close to the center of the bandgap thus changing the conduction process from interfacial Schottky to bulk Poole Frenkel and decreasing the extrinsic losses. This beneficial effect was already inferred in ceramics and thin films but we have established a clear link between the macroscopic parameters and the microscopic defect state. This model can be transferred to many high permittivity oxides.
RESUMEN
A Bruker Optics IFS 125HR Fourier transform spectrometer (FTS) and the Laboratoire de Physique Moléculaire pour l'Atmosphère et l'Astrophysique retrieval algorithm were adapted for ground based atmospheric measurements. As one of the major instruments of the experimental research platform QualAir, this FTS is dedicated to study the urban air composition of large megacity such as Paris. The precise concentration measurements of the most important atmospheric pollutants are a key to improve the understanding and modeling of urban air pollution processes. Located in the center of Paris, this remote sensing spectrometer enables to monitor many pollutants. Examples for NO(2) and CO are demonstrating the performances of this new experimental setup.
Asunto(s)
Análisis de Fourier , Análisis Espectral/instrumentación , Universidades , Algoritmos , Atmósfera/química , Monóxido de Carbono/química , Luna , Dióxido de Nitrógeno/química , Sistema Solar/química , Análisis Espectral/métodosRESUMEN
The Limb Profile Monitor of the Atmosphere (LPMA) instrument is a Fourier transform spectrometer designed to record stratospheric (and in some cases tropospheric) absorption spectra from a balloon gondola. This spectrometer operates with two-detector output optics (photoconductive HgCdTe and photovoltaic InSb, liquid-nitrogen cooled). The response of the HgCdTe detector becomes nonlinear for high photon fluxes, which is the case for solar occultation. We have designed a processing scheme, based on the minimization of out-of-optical-band spectral artifacts, to correct for the effect of nonlinearity in the useful spectral range. The method is explained, and sample results are presented for spectra recorded in different balloon flight conditions and with two different HgCdTe detectors.