Controlled Elemental Depth Profile in Sol–Gel-Derived PZT Films

Elemental depth profiles of PZT films prepared by two sol–gel formulations, differing in the zirconium precursor stabilization, were investigated by SIMS analysis. Early decomposition of the zirconium precursor yielded opposing gradients of zirconium and titanium, while simultaneous late decomposition of zirconium and titanium precursors provided profile uniformity. The gradients formed during initial crystallization are irreversible. Both types of films showed excellent hysteresis; however, uniform films exhibited a much higher dielectric constant, indicating superior piezoelectric properties. Non-uniform films displayed a complex CV pattern, consistent with an inhomogeneous structure. Finally, thermal decomposition of the individual metal precursors is crucial for controlling film uniformity.     

Fractionation of isotopically labeled peptides in quantitative proteomics.

The goal of quantitative proteomics is to examine the expression levels of all of the proteins in a biological system and recognize those that change as a function of some stimulus. Quantification is now frequently based on derivatization of peptides with isotopically distinguishable labeling agents. This study examines the extent to which isotopic forms of peptides having the same amino acid sequence are resolved by reversed-phase chromatography and assesses the degree to which resolution of these isotopically different forms of a peptide impact quantification. Three derivatizing agents were examined, the do and d3 forms of N-acetoxysuccinimide, the do and d4 forms of succinic anhydride, and the do and d8 forms of the commercial ICAT reagent Peptide mixtures from control and experimental samples were derivatized individually, mixed, subjected to reversed-phase chromatography, and analyzed by ESI-MS. When partial resolution of the isotopic forms of a peptide occurs, the largest error in assessing the true isotope ratio in a sample occurs when sampling at the extremes of a peak. Early in the elution of a peak, the sample will be enriched in the deuterated species, whereas the opposite is true at the tailing edge of a peak. Acetylated peptides showed the lowest degree of separation. Resolution of the deuterated and nondeuterated forms in this case was 0.023. This amounts to slightly over a 1-s difference in their peak maxima and can cause a typical error of +/- 6% at the leading and tailing edges of a peak. In contrast, resolution of the deuterated and nondeuterated forms of the ICAT reagent were calculated to be 0.45. This means that in a peak of 1-min width (W1/2), the peak maxima will vary by approximately 30 s, and measurement errors of -83 and +500% can occur at the leading and tailing edges of a peak. It is concluded that resolution of isotopic forms of a peptide can cause substantial quantification errors in quantitative proteomics.     

Analyzing results of impedance spectroscopy using novel evolutionary programming techniques

This paper discusses the application of evolutionary programming methods to the problem of analyzing impedance spectroscopy results. The basic approach is a “direct-problem” one, i.e., to find a time constant distribution function that would create similar impedance results as the measured ones, within experimental error. Two complementary methods have been applied and are discussed here: Genetic Algorithm (GA) and Genetic Programming (GP). A GA can be applied when a known (or desired) model exists, whereas GP can be used to create new models where the only a-priori knowledge is their smoothness and their non-negativity. GP is tuned to prefer relatively non-complex models through penalization of unnecessary complexity.     

Cathodic electrophoretic deposition of barium titanate films from aqueous solution

Cathodic electrophoretic deposition (EPD) of barium titanate from aqueous suspensions was performed on nickel substrate. Cathodic deposition allows preparation of thin layers from aqueous solution on base metal electrodes, such as Ni or Cu, without creating an intermediate oxide layer during the deposition. This opens the opportunity to prepare complex shapes of dielectric layers onto base metals for co-firing, using relatively cheap and environmentally benign aqueous EPD. Stable barium titanate colloidal suspension with a concentration of 10 g/100 mL at pH of 9.2 has been prepared for the deposition. The characteristics of electrophoretic deposition of those positively charged particles onto cathode were investigated. A uniform and dense layer was obtained for films deposited at 3 V for 2 min. The calculated film thickness for the sintered layer at these conditions was ∼1 μm. The morphology can be controlled, and in particular the pore size and distribution can be controlled via the applied voltage. At low voltage a uniform layer can be obtained whereas at high voltage a large number of macropores appears in the deposit and their size increase with the increasing of the voltage due to gas bubble formation.     

Effect of Incorporating Method of Niobium on the Properties of Doped Barium Titanate Ceramics

A series of undoped and doped barium titanate powders were prepared and examined by: X-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, particle size, ζ-potential, specific surface area, differential scanning calorimetry (DSC), impedance spectroscopy, and secondary-ion mass spectrometry. The doped samples were prepared by two different methods: (1) coating powders with chlorides and (2) mixing chlorides in a hydrothermal reactor. Different distribution profiles of the dopant atoms were observed for the two incorporation methods. Two T _C peaks were detected by DSC for samples doped by coating. Analysis of electrical measurements revealed time constant distributions that were more spread in samples that had a core–shell structure.     

Surface Composition and Imprint in CSD-Based PZT Films

Reports on PZT films often suggest the contradicting presence of Pb-deficient pyrochlore (Py) and a Pb-rich layer on the surface. We show that standard Ar⁺ ion sputtering X-ray photoelectron spectroscopy (XPS) depth profiles of PZT films artificially exhibit a Pb-rich surface, independent of actual Pb content of the chemical solution deposition solution. However angle-resolved XPS measurements reveal that films derived from solutions with 10% Pb excess, which give rise to Py surface grains, actually have the expected Pb-deficient surface layer. Alternatively, films derived from solutions with 30% Pb excess are Py free and have Pb-rich surface layer. The Pb-rich films show an increased imprint effect with increasing Pb content.     

Electrochemical Impedance Analysis of SOFC Cathode Reaction Using Evolutionary Programming

Investigation of the cathode reaction in solid oxide fuel cells (SOFC) by impedance spectroscopy (IS) measurements using evolutionary‐based programming analysis is demonstrated. In contrast to the conventional analysis methods used for impedance spectroscopy measurements, e.g., equivalent circuits, the impedance spectroscopy genetic programming (ISGP) program seeks for a distribution of relaxation times that has the form of a peak or a sum of several peaks, assuming the Debye kernel. Using this method one finds a functional (parametric) form of the distribution of relaxation times. A symmetric cell configuration of Pt|LSCF|GDC|LSCF|Pt was examined using IS measurements combined with I–V measurements. Different samples at different temperatures and different oxygen partial pressures were examined in order to investigate their influence on the oxygen reduction reaction. The resulting IS data was analyzed using the ISGP program and the resulting peaks constructing the distribution of relaxation times were assigned for the different processes that occur at the cathode side. The activation energies as well as the dependence of the processes on the oxygen partial pressure were also evaluated.     

Controlling deuterium isotope effects in comparative proteomics

This paper focuses on identifying structural features responsible for resolution of heavy isotope coded peptides during reversed-phase chromatography. This was achieved by using labeled coding agents that varied in structure, number of deuterium atoms, placement of deuterium in the coding agent, and the functional group targeted by the reagent. Six coding agents were examined. Deuterated versions of the coding agents studied included succinic anhydride-2H4, acetic acid 2,5-dioxopyrrolidin-1-yl ester-2H3, propionic acid 2,5-dioxopyrrolidin-1-yl ester-2H5, pentanoic acid 2,5-dioxopyrrolidin-1-yl ester-2H9, [3-(2,5-dioxopyrrolidin-1-yloxycarbonyl)-propyl]-trimethylammonium chloride-2H9, and the commercial ICAT-2H8 reagent. It was found that these labeling agents vary widely in both their absolute and relative contribution to the chromatographic isotope effect. Relative effects were evaluated by normalizing resolution for the number of deuterium atoms in the derivatized peptide. The single, most dominant effect was the placement of deuterium atoms relative to hydrophilic functional groups in the coding agent. It was concluded that the probability of a deuterium atom interacting with the stationary phase of a reversed-phase chromatography (RPC) column and impacting resolution is greatly diminished by placing it adjacent to a hydrophilic group, as explained by solvophobic theory. But peptide size and coding agent size were also seen to correlate inversely with the magnitude of the isotope effect. This effect was explained as being due to the relative size of the coding agent versus that of the coding agent-peptide conjugate.     

Analysis of Impedance Spectroscopy Data—Finding the Best System Function

Impedance spectroscopy gains much attention as a non-destructive analysis technique in many areas of materials science and device manufacturing. While it is relatively easy to collect data, the correct analysis or the data interpretation is not a straightforward task. In this paper, a novel analysis technique that provides a simple mean to identify the best system function is shown.A new taxonomy of all the possible circuit models that are based on RC lumped elements is given. The taxonomy divides the various circuit models into groups of increasing complexity. Its order and family, where for RC elements there are four different families, identify each group. A black box, rather than a pre-assumed circuit model, represents the sample under test (SUT). The simplest group (order and family) that describes the SUT accurately within the experimental limitations can be found in a single experiment. In some cases, the best circuit model within the group can also be found by investigating the behavior of the SUT under various changes (i.e., temperature, radiation, other environmental conditions, sample construction, etc.).The technique is demonstrated on various circuits with lumped capacitors and resistors. This is done both on actual systems and on synthetic data with artificial noise. A comparison of this method with a standard Cole-Cole identification demonstrates the power of the new approach.